I've modified the player side rules for Classic D&D (or Labyrinth Lord if you don't have access to the original game). All rules for races, classes, equipment, and spells presented here supersede anything in those books. Details for all will be provided below.

Changes:

Races
Character Race and Class are separate.
Standard Races: Human, Dwarf, Elf, Halfling
Extra Races: Gnome, Half-Elf, Half-Orc, Dragonborn (because my son loves them), Changeling (because many players in my 5E game love tieflings)

Classes
Four main classes, each with two subclasses, for a total of 12.
Cleric (Cavalier, Druid)
Fighter (Berserker, Ranger)
Magic-User (Bard, Illusionist)
Thief (Acrobat, Assassin)

Human characters can dual class, demi-human characters can multiclass (as per AD&D), but with slightly different selections by race.

Equipment
A few small changes to weapons, armor, and other gear. Mostly additions. I use ascending AC rather than descending, armor adds to AC rather than subtracting.

Spells
I've simplified a few spell effects. In general this will benefit you players, as it will allow you to be creative with spell use. Just like in the good old days, I don't mind if you find exploits for certain spells and use them to your advantage. That's smart play.

See below for complete details.
This message was last edited by the GM at 00:23, Wed 26 Sept 2018.

Human:
* No ability score minimums
* All classes available, with no level limits
* Survival: When rolling for hit points (2nd level and higher), roll twice and take the better result
* Dual Classing: You can switch to another class provided you are between 3rd and 8th level in your current class, and have at least a 13 in the prime requisite(s) of the new class. You keep your current hit points, but otherwise act as a 1st level character of the new class. No XP is earned for that adventure if older class abilities other than hit points are used. Once you reach 3rd level in the new class, all abilities of the old class become available again along with your new abilities.
* Languages: Common, +any one language

Dwarf
* Minimum 9 Constitution
* Berserker (8), Cavalier (6), Cleric (8), Fighter (12), Thief (6)
* Multiclass: Cleric/Fighter, Cleric/Thief, Fighter/Thief
* Senses: Infravision 60', Detect Traps, Shifting Walls, Sloping Passages, New Construction 1-2 on 1d6, Listening 1-2 on 1d6
* Toughness: +4 bonus to all Saving Throws
* Languages: Common, Dwarf, Gnome, Goblin, Kobold
* Restrictions: May not use two handed swords, longbows, or any pole arm.

Elf:
* Minimum 9 Intelligence
* Bard (12), Fighter (10), Magic-User (10), Thief (8)
* Multiclass: Bard/Fighter, Bard/Thief, Fighter/Magic-User, Fighter/Thief, Magic-User/Thief
* Senses: Infravision 60', Detect Secret doors 1-2 on 1d6, Listening 1-2 on 1d6
* Immunity: Immune to ghoul paralysis
* Languages: Common, Elven, Gnoll, Hobgoblin, Orc

Halfling
* Minimum 9 Dexterity, 9 Constitution
* Acrobat (8), Druid (6), Fighter (8), Ranger (10), Thief (12)
* Acrobat/Fighter, Druid/Ranger, Fighter/Thief, Ranger/Thief
* Senses: Listening 1-2 on 1d6
* Hiding: Hide outdoors 1-9 on 1d10, hide indoors 1-2 on 1d6
* Combat Bonus: +1 to hit with ranged/thrown weapons, +2 AC vs large opponents
* Lucky: +4 bonus to all Saving Throws
* Languages: Common, Halfling, +any one language
* Restrictions: May not use battle axes, two handed swords, longbows, morning stars, heavy crossbows, or any pole arm. May use bastard swords but only two handed.

Gnome
* Minimum 9 Constitution
* Bard (8), Fighter (6), Illusionist (12), Thief (8)
* Multiclass: Bard/Thief, Fighter/Illusionist, Fighter/Thief, Illusionist/Thief
* Senses: Infravision 90'
* Beast Speech: communicate with small birds and rodents
* Combat Bonus: +1 to hit when fighting goblins/kobolds, +2 AC vs large opponents
* Innate Magic: +2 bonus to all Saving Throws
* Languages: Common, Gnome, Dwarf, Kobold, Goblin
* Restrictions: May not use battle axes, two handed swords, longbows, morning stars, heavy crossbows, or any pole arm. May use bastard swords but only two handed.

Half-Elf
* No ability score minimums
* Assassin (6), Cleric (6), Druid (10), Fighter (8), Magic-User (8), Ranger (8), Thief (10)
* Multiclass: Cleric/Fighter, Cleric/Fighter/Magic-User, Cleric/Magic-User, Cleric/Magic-User/Thief, Cleric/Ranger, Fighter/Thief, Magic-User/Thief, Ranger/Thief
* Senses: Infravision 60', Listening 1-2 on 1d6
* Versatility: choose either Human Survival ability or Elf detect secret doors and ghoul immunity abilities
* Languages: Common, Elven, Hobgoblin, Orc, +any one language

Half-Orc
* Minimum 9 Strength or 9 Dexterity
* Acrobat (6), Assassin (12), Berserker (10), Cavalier (6), Cleric (6), Fighter (10), Thief (6)
* Multiclass: Acrobat/Fighter, Assassin/Cleric, Assassin/Fighter, Cleric/Fighter, Fighter/Thief
* Senses: Infravision 60', sense of smell gives +1 to track if a Ranger
* Disguise: Pass as fully human or fully orcish 1-4 on 1d6, pass as opposite sex 1-2 on 1d6, pass as other demi-human/humanoid race 1 on 1d6
* Languages: Common, Orc, Giant, +any one language

Dragonborn
* Minimum 9 Strength, 9 Charisma
* Cleric (10), Fighter (10), Magic-User (8), Thief (8)
* Multiclass: Cleric/Fighter, Cleric/Magic-User, Cleric/Thief, Fighter/Magic-User, Fighter/Thief, Magic-User/Thief
* Resistance: -1 point of damage per die and +2 to saves vs one: cold, acid, poison gas, lightning, or fire (choose one)
* Breath Weapon: deals 1d6+1 damage of resistance type, opponents may Save vs Breath Weapon for half damage, usable once per day.
-Cold/Fire: 15' long, 10' wide cone
-Acic/Lightning: 5' wide, 25' long line
-Poison Gas: 10' cube
* Languages: Common, Dragon

Changeling
* Minimum 9 Wisdom
* Cleric (12), Fighter (6), Illusionist (8), Magic-User (6), Thief (6)
* Multiclass: Cleric/Fighter, Cleric/Illusionist, Cleric/Thief, Illusionist/Thief, Magic-User/Thief
* Senses: Infravision 60'
* Heritage: cast one cleric spell once per day depending on heritage (or alignment):
-Angelic (Lawful): light
-Demonic (Chaotic): darkness
-Fey (Neutral): cause fear
* Languages: Common, any 1

Multiclassing: Demi-humans with two or three classes divide all XP earned evenly between the classes before applying any bonuses for high prime requisite scores. Prime requisite bonus XP is only added to the qualifying class(es). When rolling for hit points, roll each die and divide the result by the number of classes. Record fractional results.
-Multiclass Clerics can use any weapons allowed by their other class.
-Multiclass Illusionists and Magic-Users can wear any armor allowed by the other class and still cast spells.
-Multiclass Druids are still bound by the armor restrictions of the class.
-Multiclass Thieves may wear any armor allowed by the other class, but cannot perform Climb Sheer Surfaces, Remove Traps or Move Silently skills while in armor heavier than leather.
This message was last edited by the GM at 00:36, Wed 26 Sept 2018.

Each class description tells you just the basics: the advancement chart, prime requisite, minimum ability scores needed, hit dice, saving throws, armor/weapons allowed, and any special abilities. I'm assuming you've all played D&D enough to recognize what these are without the flavor text.

Classes and Subclasses:
Cleric: Holy warriors with magical abilities.
-Cavalier: Mounted knights with some magical abilities.
-Druid: Guardians of nature with magical abilities.
Fighter: Warriors of all types.
-Berserker: Savage warriors who enter a blood-lust in battle.
-Ranger: Warriors who patrol the wilds to protect civilization.
Magic-User: Magicians of all types.
-Bard: Magicians and sages. (*note - my bards are NOT minstrels)
-Illusionist: Masters of using magic to deceive.
Thief: Specialists at dungeon delving and procuring treasure.
-Acrobat: Specialists in movement and unarmed combat.
-Assassin: Stealthy killers.

Each class is presented in its own post below, in alphabetical order.
This message was last edited by the GM at 08:59, Tue 26 Sept 2017.

Acrobat

Advancement Table
*Name Level

Prime Requisite: Wisdom and Dexterity. If both are 13+, +5% XP. If both are 16+, +10% XP
Minimum Scores: 13 Strength
Hit Dice: 1d8+Con adjustment to 9th level, +1 hit point (no Con adjustment) from level 10
Saving Throws

Armor: None, no shield
Weapons: Bola, club, dagger, net, quarterstaff, shortsword, sickle, sling, spear, whip

Special Abilities
Combat: Acrobats have two combat abilities.
Unarmed Fighting: Acrobats can punch or kick for the damage listed on the experience table.
Defense: Acrobats gain a bonus to AC as shown on the experience table. This represents dodging and deflecting blows.
Jump: Acrobats can jump (high or long) double the distance of a normal character. If using a 10' pole, quarterstaff or spear to pole vault, they can jump three times as high, or four times as far.
Thief Skills: Acrobats can Find/Remove Traps, Hide in Shadows and Move Silently as a thief of equal level. They may not Open Locks, Hear Noise, Read Languages, or Use Magic Scrolls abilities. They may not Backstab.
Acrobatics: Acrobats can balance on any surface, climb sheer surfaces, contort their body, and tumble. One check is needed for each activity.
Balance: The acrobat can cross tightropes, fight on ice without falling, etc.
Climb: The acrobat may climb sheer walls without tools or ropes. Check once for every 100' or less climbed. Failure results in no progress. If attacked while climbing, the acrobat falls unless they make a save vs. paralysis.
Contortion: The acrobat can escape from bindings or squeeze through tight passages at least large enough for the character's head to fit into.
Tumble: The acrobat can tumble through enemy lines without being hindered, flip through a trapped area without setting off the trap, etc.
This message was last edited by the GM at 14:32, Thu 28 Sept 2017.

Assassin

Advancement Table
*Name Level

Prime Requisite: Dexterity and Charisma. If either is 13+, +5% XP. If both are 13+, +10% XP
Minimum Scores: 13 Intelligence
Hit Dice: 1d8+Con adjustment to 9th level, +2 hit points (no Con adjustment) from level 10
Saving Throws

Armor: Any armor, may use a shield (Metal armors hinder use of thief skills)
Weapons: All weapons

Special Abilities
Combat: Assassins may backstab as a thief. If the assassin has at least 1 turn to study an opponent outside of combat and then is in a position to backstab, they may make a special assassination attempt. If the first attack hits, the target must save vs. death ray or die. If the target saves, the attack still counts as a backstab.
Disguise: Assassins have a 4 in 6 chance to create a disguise to blend in with a certain group (a generic soldier, baker, fisherman, etc.). At 4th level, they may attempt a disguise an another race of similar size. At 8th level, they can attempt to create a disguise that appears to be a specific individual, another sex, or a dissimilar race.
Languages: Assassins gain a bonus language at 1st level. At 4th, 8th, and 12th level, they learn new bonus languages, which may be alignment languages if desired. Use of these bonus languages is not perfect, and there is a 1 in 6 chance the assassin may misunderstand when listening or reading, or may fail to communicate intelligibly when speaking or writing.
Thief Skills: Assassins function as a thief with regard to the following skills: Open Locks, Pick Pockets, Move Silently, Climb Sheer Surfaces, and Hide in Shadows. Assassins do not gain the Find/Remove Traps, Listen, Read Languages, or Use Scrolls abilities. Picking pockets, moving silently and climbing in scale or chain imposes a -20% penalty, banded and plate impose -40%. A shield imposes an additional -10% penalty to picking pockets and climbing.
This message was last edited by the GM at 14:33, Thu 28 Sept 2017.

Berserker

Advancement Table
*Name Level

Prime Requisite: Constitution. If 13+, +5% XP. If 16+, +10% XP
Minimum Scores: 13 Strength
Hit Dice: 1d12+Con adjustment to 9th level, +3 hit points (no Con adjustment) from level 10
Saving Throws

Armor: Any armor, may use a shield
Weapons: All weapons

Special Abilities
Combat: Berserkers gain two unique advantages in combat:
Offense: When fighting human, demi-human or humanoid opponents, they gain a bonus of +2 to hit, and are immune to fear effects while they receive this bonus to attack.
Defense: Berserkers gain a +2 bonus to Armor Class when wearing leather or no armor, in addition to any bonus from high Dexterity. A shield may also be used.
Languages: In addition to the Common tongue, all berserkers speak their native language. However, the berserker is illiterate in all known languages (may not use magic scrolls, can only read pictorial information from maps). If the berserker has high intelligence, other languages may be known as normal, or the berserker can gain literacy in place of an extra language.
This message had punctuation tweaked by the GM at 14:33, Thu 28 Sept 2017.

Bard

Advancement Table
*Name Level

Prime Requisite: Intelligence. If 13+, +5% XP. If 16+, +10% XP
Minimum Scores: 13 Wisdom
Hit Dice: 1d6+Con adjustment to 9th level, +1 hit point (no Con adjustment) from level 10
Saving Throws

Armor: Leather, scale and chain armor, may use a shield
Weapons: Any one-handed melee weapon, and all missile weapons

Special Abilities
Skills: Bards can Hear Noise and Read Languages as a thief, but Read Languages can be used from 1st level and increases as the bard gains levels.
Lore: Bards have a chance to know the function of an unidentified magic item, name and history of a special item, or have clues and rumors (not necessarily true) about dungeons, important NPCs, and monsters.
Spells: Bards cast spells as Magic-Users once they reach 2nd level, and require a spellbook. They start with a spellbook containing 1 spell, and each level can add one spell of any level they can cast to the spellbook. They may add any Magic-User spells found on scrolls if Read Magic is used. Additionally, Cleric, Druid or Illusionist spells found on scrolls can be added to their spellbook if the scroll becomes usable via the Knack ability.
Knack: At 4th level, bards may try to use magic items normally prohibited. When a bard attempts to use such an item, roll 2d6. A result of 9 or greater means the bard can use the item for one Turn. A result of 4 or less is a magical mishap of some sort, determined by the DM.
Languages: In addition to the Common tongue, all bards speak dwarf, elf, halfling and any one other language. If the bard has high intelligence, other languages may also be known.
Magic Item Creation: At Name Level, any type of magic item may be created.
This message had punctuation tweaked by the GM at 14:34, Thu 28 Sept 2017.

Cavalier

Advancement Table
*Name Level

Prime Requisite: Strength and Wisdom. If both are 13+, +5% XP. If both are 16+, +10% XP
Minimum Scores: 13 Charisma
Hit Dice: 1d10+Con adjustment to 9th level, +2 hit point (no Con adjustment) from level 10
Saving Throws

Armor: Any armor, may use a shield
Weapons: Any weapon

Special Abilities
Combat: Cavaliers have two special abilities in combat.
Mounted Combat: Cavaliers gain a +1 bonus to hit when engaged in mounted melee combat. In addition, their mount may always make use of all of its natural attacks in a round, and the cavalier suffers no penalties to attack while the mount is attacking.
Destroy the Unholy: A cavalier's weapons can always damage creatures that can only be hit by silver or magic, even if the weapons are not enchanted.
Turn Undead: Beginning at 4th level, a cavalier can turn undead as a cleric of 1/3 his cavalier level. Refer to the cleric description for details.
Spells: Beginning at 4th level, a cavalier can cast clerical spells.
Magic Item Creation: At Name level, cavaliers can craft magical melee weapons and armor.
This message had punctuation tweaked by the GM at 14:35, Thu 28 Sept 2017.

Cleric

Advancement Table
*Name Level

Prime Requisite: Wisdom. If 13+, +5% XP. If 16+, +10% XP
Minimum Scores: None
Hit Dice: 1d8+Con adjustment to 9th level, +1 hit point (no Con adjustment) from level 10
Saving Throws

Armor: Any armor, may use a shield
Weapons: Bludgeoning weapons only (blackjack, bola, club, flail, mace, morning star, net, sling, staff, throwing hammer, war hammer, whip)

Special Abilities
Spells: At 2nd level, clerics gain the ability to cast magical spells. Clerics must meditate to prepare their spells for the day. The number of spells of each level that a cleric may prepare each day are given in the Cleric Experience Table above. Clerics may prepare any spells they wish from the list of cleric spells of the appropriate level. They do not have spellbooks.
Turning Undead: Clerics can force Undead to flee, and at higher levels to destroy them. Clerics may attempt to turn once per round. Roll 2d6 vs. the target number. A 'T' is automatic success, a 'D' is 'destroy.' If the attempt is successful, 2d6 Hit Dice of the Undead flee (or are destroyed). A cleric may continue Turning as long as the attempts succeed.
Turn Undead Table
Magic Item Creation: At Name level, clerics can craft any magical items which they can use.
This message was last edited by the GM at 14:35, Thu 28 Sept 2017.

Druid

Advancement Table
*Name Level

Prime Requisite: Wisdom and Dexterity. If both are 13+, +5% XP. If both are 16+, +10% XP
Minimum Scores: 13 Strength
Hit Dice: 1d8+Con adjustment to 9th level, +1 hit point (no Con adjustment) from level 10
Saving Throws

Armor: None, may use a wooden or hide shield
Weapons: May only use wooden, stone or organic weapons (typically one die size smaller damage than a metal weapon of the same type)

Special Abilities
Spells: Druids can cast magical spells. Druids must meditate to prepare their spells for the day. The number of spells of each level that a druid may prepare each day are given in the Druid Experience Table above. Druids may prepare any spells they wish from the list of druid spells of the appropriate level. They do not have spellbooks.
Shape Shifting: Druids can shapeshift into an animal form. The druid gains the AC, attacks, damage, and movement of the animal, and retains their own hit points, chances to hit, and saving throws. Druids in animal form may not cast spells until they reach higher levels. The animal form lasts for one Turn. The druid consults the chart below to see the maximum hit die type that can be assumed. The druid rolls 2d6 and must meet the number rolled or better. An A is an automatic success, and an A+ means the druid may cast spells while in animal form. If a roll to shapeshift fails, the druid may not try again for one hour.
Shapeshifting Chart
Languages:  In addition to the Common tongue, druids speak the pixie and centaur languages.
Magic Item Creation: At Name level, druids can craft any magical items which they can use.
This message was last edited by the GM at 14:36, Thu 28 Sept 2017.

Fighter

Advancement Table
*Name Level

Prime Requisite: Strength. If 13+, +5% XP. If 16+, +10% XP
Minimum Scores: None
Hit Dice: 1d10+Con adjustment to 9th level, +2 hit points (no Con adjustment) from level 10
Saving Throws

Armor: Any armor, may use a shield
Weapons: All weapons

Special Abilities
Combat Style: All fighters select one combat style at first level. They gain an additional style at 4th, 8th, and 12th levels.
Dual Weapons: Using two melee weapons, the fighter does not suffer the -2 penalty to hit.
Jousting: When charging with a lance, the opponent has a -4 penalty to avoid being unhorsed by the fighter's attack.
Missile Weapon: Using any missile weapon, the fighter may add their Dex bonus to damage.
Single Weapon: Using a one-handed weapon and no shield, the fighter may Save vs. Wands to deflect an attack that would otherwise hit once per round.
Sword & Board: Using a one-handed weapon and shield, the fighter gains an additional +1 bonus to AC.
Thrown Weapon: Using a thrown weapon, the fighter doubles the range of the weapon and uses Str and Dex to modify the hit and damage rolls.
Two-handed Weapon: Using a two-handed melee weapon, the fighter suffers no initiative penalties.
Unarmed: The fighter's unarmed attacks deal 1d4 damage. No matter what weapons the fighter is using, if their normal attack misses, they may make an additional unarmed strike.
Weapon Specialization: The fighter chooses any one weapon, and gains +1 to hit and +2 to damage with that weapon.
Combat Options: At 9th level, the fighter can make two attacks in a round. Instead of making two attacks, the fighter can choose to make a single Smash Attack. The fighter takes a -5 penalty to the attack roll. If the attack hits, the fighter's entire Strength score is added to the damage, along with all normal bonuses (including Strength modifier).
This message was last edited by the GM at 07:09, Wed 06 Dec 2017.

Illusionist

Illusionist Advancement Table
*Name Level

Prime Requisite: Intelligence and Charisma. If both are 13+, +5% XP. If both are 16+, +10% XP.
Minimum Score: Dexterity 13
Hit Dice: 1d4+Con adjustment to 9th level, +1 hit point (no Con adjustment) from level 10
Saving Throws

Armor: None, may not use shields
Weapons: Any one-handed melee or thrown weapon, but no missile weapons

Special Abilities
Spells:  Illusionists can cast spells as a magic-user, and must keep a spellbook. Illusionists start play with a spell book containing the spell Read Magic, and at least one other 1st level spell. When the illusionist goes up a level, one additional spell of any level that can be cast is added to the book. Illusionists follow all of the rules for magic-users regarding spells, spellbooks, and spell research.
Thief Skills: Illusionists may Hide in Shadows, Move Silently, and Pick Pockets as a thief of equal level. See the thief class (below) for more details.
Magic Item Use: Illusionists may use any magic items usable by magic-users. They may use magical one-handed melee or thrown weapons.
Detect Illusions: Because illusionists work with illusion magic extensively, they gain a +2 bonus to saving throws with regard to illusions if a save is normally allowed. If no save is normally allowed, they gain a saving throw but without the bonus.
Magic Item Creation: At 1st level, an illusionist can create magical scrolls of spells within his spell book, at a cost of 1 week and 100 gp per spell level. At Name Level, the illusionist can create any magical items which they may use.
This message was lightly edited by the GM at 14:37, Thu 28 Sept 2017.

Magic-User

Illusionist Advancement Table
*Name Level

Prime Requisite: Intelligence. If 13+, +5% XP. If 16+, +10% XP.
Minimum Score: None
Hit Dice: 1d4+Con adjustment to 9th level, +1 hit point (no Con adjustment) from level 10
Saving Throws

Armor: None, may not use shields
Weapons: Dagger and staff only

Special Abilities
Spells:  Magic-users have the ability to cast magical spells. Magic-users must study their spellbooks to prepare their spells for the day. The number of spells of each level that may be prepared each day are given in the Magic-User Experience Table. Magic-users may prepare any spells they wish from their spellbooks of the appropriate level.
Magic-users start play with a spell book containing the spell read magic, and at least one other 1st level spell. The magic-user gains one additional first level spell for each point of Intelligence bonus. When the magic-user goes up a level, one additional spell of any level that can be cast is added to the book. The magic-user may additionally increase the number of spells in his or her spell book in one of three ways:
1. Copying scrolls
2. Copying another spell book
3. Magical research
Magic Item Creation: At 1st level, a magic-user can create magical scrolls of spells within his spell book, at a cost of 1 week per spell and 100gp per spell level. At Name Level, all magic items, save those only usable by bards, clerics, druids, or illusionists, may be created.
This message was lightly edited by the GM at 14:38, Thu 28 Sept 2017.

Ranger

Advancement Table
*Name Level

Prime Requisite: Dexterity and Wisdom. If both are 13+, +5% XP. If both are 16+, +10% XP
Minimum Scores: 13 Constitution
Hit Dice: 1d8+Con adjustment to 9th level, +2 hit point (no Con adjustment) from level 10
Saving Throws

Armor: Leather armor, may use a shield
Weapons: Any weapon

Special Abilities
Combat:  Rangers train to fight ettins, bugbears, giants, gnolls, goblins, hobgoblins, kobolds, ogres, orcs and trolls. They get a +1 bonus to attack rolls against these creatures. At 4th level they also gain a +2 bonus to damage against these creatures. At 8th level, the attack bonus increases to +2 and the damage bonus increases to +4.
Ranged Weapons:  Rangers also gain a +1 bonus to hit when using any missile or thrown weapons.
Tracking:  Rangers are adept at tracking others. When outdoors, they may track successfully on a 1-9 on 1d10 (unless much time, bad weather, or magic hinders this). Indoors and in dungeons, they may track, but are less successful, only tracking on a 1-2 on 1d6. Tracking checks must be made twice per day outdoors, and once per hour indoors. The ranger must have observed the creatures (or be directed to the general area by someone who has) within one tracking time period (12 hours outdoors, 1 hour indoors) to begin tracking.
Survival: Rangers have double the chances to forage food while traveling through the wilderness, and if successful forage double the amount. If the party becomes lost, the ranger has a 2 in 6 chance to notice this per day and discover the correct orientation of the party.
Spells: Beginning at 4th level, a ranger can cast druid spells.
Magic Item Creation: At Name level, rangers can craft magical missile weapons and ammunition.

Thief

Advancement Table
*Name Level

Prime Requisite: Dexterity. If 13+, +5% XP. If 16+, +10% XP
Minimum Scores: None
Hit Dice: 1d6+Con adjustment to 9th level, +2 hit points (no Con adjustment) from level 10
Saving Throws

Armor: Leather armor, may not use a shield
Weapons: All one handed melee weapons and all missile weapons

Special Abilities
Open Locks: Thieves can open locked doors, treasure chests, etc. with thieves' tools.
Find/Remove Traps: Thieves detect traps easily.  Only one attempt can be made to remove a trap.
Pick Pockets: Thieves can lift small objects from others. Subtract 5% per level or hit die of the victim (minimum 0%, maximum 99%).  If the thief fails by double, the victim notices.
Hide in Shadows: Thieves may hide in nothing but shadows. This always seems successful to the thief.
Move Silently: Thieves may move completely silently. This always seems successful to the thief.
Climb Sheer Surfaces: Thieves may climb sheer walls without tools or ropes. Check once for every 100' or less climbed. Failure results in no progress. If attacked while climbing, the thief falls unless they make a save vs. paralysis.
Hear Noise: Thieves can detect noises well.
Backstab: If a thief sneaks up on a victim and makes a melee attack, the thief gets +4 to hit and x2 damage. At 6th level, the damage increases to x3, and at 11th, to x4.
Read Languages: At 4th level, thieves have an 80% chance to read any non-magical writings, including written codes and secret languages.
Cast Scrolls: At 10th level, thieves have a 90% chance to cast spells from scrolls. If the attempt fails, it will backfire with an unexpected result.
This message was lightly edited by the GM at 14:15, Fri 29 Sept 2017.

I should probably mention this here. There are a lot of locked doors and chests and whatnot in the dungeon.

I haven't placed keys for every single lock. I'm not going to track every single key and lock. Ain't no one got time for that, as the internet memes say.

Instead, keys in the megadungeon work like in classic video games such as Gauntlet. If you find a key, it will open one lock (then disappear). It doesn't matter what lock you try it on. It will open that lock.

Keys are a resource. Use them wisely.