Immersive Ink

Without a torch, Mero cannot advance farther into the room.

Morin enters and casts lantern-light about — especially towards the left-hand wall, where he surmises there should be another door. But he pauses before investigating further.

"A word before is worth two behind! This chamber is vast; in our efforts to explore it, we must not scatter ourselves like grains of sand on the wind. Some small group should approach the pit and report back what they see. Only then should another group approach yonder door to our right and open it. Such is my recommendation."

Chiron, lighting the way, and Orim move cautiously some 30ft into the room, toward the pillars. Meanwhile Morin, with lantern, comes 10ft into the room to clear the way for others.

Soon enough, Chiron and Orim are among the tall pillars, from where they can see 'tis another 20ft or so beyond these to the lip of the dark, diamond-shaped hole that is itself about 30ft across. Looking up, they espy a great, tall space above the pillars, from whence a dim blue glow prevails upon them...

Chiron takes a close look at the pillars, to see if they have any writing or runes on them.

Then he takes a peek into the hole.

Lemmi drifts silently into the room, but hangs back from the lantern-bearers and sticks to the shadows. She keeps a wary eye out for any unwelcome guests

Orim takes note of the floor around the hole, looking for any irregularities before he steps forward to look in.

With Chiron, Lemmi, Orim and Morin moving about the room proper, I will assume that everyone in the marching order ahead of them must have shuffled into the entry of the room to make way for them. Everyone behind them in the marching order is still in passage way.

So. According to the Parallel Company's double file marching order, the only figures behind Morin the Hooded are the last four Boggsmen.

Therefore, we have Mero, Walfried, the first two Boggsmen, and Boggs himself (so, five figures) loitering just inside the doorway.
Chiron, Lemmi, Orim and Morin are more advanced into the room.
Four more Boggsmen remain in the passage outside the room.

Chiron examines the nearest pillar; it looks like old stone, pitted with chips and cracks and overgrown with verdigris, but there are no purposeful marking that he can see. Meanwhile, Orim puts his eye to the 20ft broad approach to the lip of the dark hole; it appears firm and sound, excepting perhaps a few flags at the very edge.

Satisfied, the pair approach the dark, diamond shaped hole to peer over the edge. They see the fissure drops perhaps 50--60ft to a spill of treasure on the floor below! No sooner have they grasped this than a sneering voice issues from above them: "GRa GRAAaaaJHA, FJHUC KR-AZZS MJHA??"

Immediately looking up, the brave pair espy a lion-sized knot of aphotic serpentine coils, clinging improbably to the chimney wall 30ft above them! Dark scales glimmer as the serpent arcs glide silently in continuous motion, its awful crocodile-face regards them steadily through alien eyes...

The players have forced the door, so there is no chance of them surprising the monsters.
Will the monsters surprise the players? 1d6=3, so no. Bummer.

Okay then, so the encounter distance would be 2d6=8, so 80ft. Okay, in the context of the chamber, that can be 80ft from the main company near the doorway.

Do the monsters speak common? 1d6=?
Initial reaction check 2d6=?

So now we dive down to the combat-turn timescale people.

At this point, only Chiron and Orim have seen the monster. Everyone else in the room will have heard... something.

Your orders?