OOC: You can only Take 10 when you're not being threatened or distracted (unless you have some special ability that lets you do it). Given the possibility of a giant glass monster rising beneath you... So, you'll need to roll. I'll also consider how high you jump over it.
Gurgun, I'll place you depending on how well you roll.
Balrok, it might better if you just charge it from the front. Then you and Gurgun can flank it.
As you've been studying up on shardcasters and recently attempted this same fight, I'll assume you know its range of detection and activation speed, so you get a surprise round (especially for these jumping shenanigans). The shardcaster begins to rise from the ground, but is surprised, ie. flatfooted.
The adventurers waited in the Nexus, just inside the door and just outside the area that the shardcaster had been programmed to defend: the bridge.
They readied their weapons and cast their spells and laid their plans. They'd done all they could do to prepare against this glass behemoth. Hopefully they'd done enough.
Gurgun lead the way, sprinting out of the door and down the length of the bridge, ready to vault the creature as it emerged from the ground. The others spilled out behind him, ready to follow and attack while the shardcaster activated.
The bridge rumbled and shook, and there it was again, climbing up out of the centre of the bridge, just as before. Fortunately it was just as cracked and fractured as they'd left it; it hadn't healed. The jagged maw roared as glass screeched against glass.
Surprise Round:
G: Gurgun Nightwhisper (position pending)
S: Slove
J: Jorn Brightcaller
B: Balrok
S: Shardcaster
Effects:
Gurgun:
enlarge
Jorn:
alter form (Tren)
Initiative:
17 - Shardcaster (surprised)
16 - Slove
12 - Gurgun
19 - Balrok
6 - Jorn