I'm reading an old adventure that provides old-style one-line monster summaries like:

Cave Bear: AC 5, HD 7, hp 33, #AT 3, D 1-8/1-8/2-12, MV 120' (40'), save F4, ML 9, AL N.

I think I understand each of those entries except for ML. What is that? Does it tell the GM what the creature adds to its attack rolls, because I don't see that listed anywhere, unless it's tied to hit dice.

In reply to engine (msg # 1):

I believe it's "Morale". It was a thing in basic and advanced 1e and 2e.

In reply to Mr_Qwerty (msg # 2):

Right of course. Thanks. And I found a table in the adventure linking HD to to-hit.

Morale is a rule I still use in my D&D games to this day, regardless of edition. I find it makes combat less exhausting, less time-consuming, and more believable. It opens up options for player character tactics that they normally wouldn't consider when every enemy routinely fights to the death - for example, PCs may try intimidation tactics, parleying (especially when paired with the old reaction rules), negotiating for a truce if things are going poorly for both sides, convincing enemies to surrender and lay down their arms, etc. It also helps to prevent the "five minute workday" issue, since fights don't always exhaust everyone's spells, potions, and hit points.

It also makes a real difference what type of enemy the PCs are fighting. Morale rules make fighting skeletons and fanatic cultists much more frightening, and give players good reason to worry about how seasoned and disciplined their foes are (like the difference between fighting a group of squabbling bandits and a phalanx of war-hardened legionnaires).

If I remember correctly, the number provided is what the monster needs to roll below (on 1d12 or 2d6?) in order to keep fighting after first blood, half of their number being taken out, and so on.

In reply to muledonkey (msg # 4):

I've been winging morale since second edition, there's no need for a specific threshold for it.

In reply to muledonkey (msg # 4):

Correct, I've used it a lot with 4e to make combat encounters shorter. I used simple Saving Throw with situational modifiers - it worked very well.