Thankfully, this chamber isn't very high according to DP, with barely more clearance than Roland needs to stand at his full height. It might be flying, but it's not got room enough to gain any altitude. The width of the room is unknown, but it can't be too large going by the description DP gave us.
Everyone is Hasted, so on top of the various combat bonuses, we each get a +30 foot movement speed boost. Given the limited dimensions of the space we're in, that speed means all of our melee combatants will easily be able to reach it to attack for at least one more round.
[X] You Shall Not Pass!
-[X] Inge uses Conduit Surge to boost her caster level by 1d4-1 and targets it with a Snowball spell, trying to hit it before the melee fighters can reach it if possible
-[X] Esha targets the Formless with a Magic Missiles spell.
-[X] Zaia refrains from using a Firebomb unless the Formless manages to get past everyone and is heading for the exit.
-[X] Roland uses his Challenge ability as a Swift Action, then moves to intercept the Formless, Power Attacking as he does so before it can reach the exit. He will specifically target one of its wings, the one Swift Pebble damaged if possible, to cripple its ability to fly.
-[X] Tom and Wanderer move to intercept the Formless, Power Attacking and, if necessary, focusing their efforts on the same wing as Roland.
-[X] The Zentragt Charges the Formless, attacking in an attempt to Grab it and Drag it down to the floor. The Formless' Freedom of Movement makes Grappling impossible, but Pteranodon's aren't built for supernatural flight, so having a Large-sized battle-bear grab a hold of of a wing or talon should be enough to force it to the ground for a moment, assuming it's attack succeeds, of course.
-[X] Swift Pebble continues her in-flight vivisection, using Piranha Strike and Sneak Attack (it might not be technically Flanked yet, or Flat-Footed, but I think this situation calls for it). She'll also benefit a +1 attack bonus due to her Limb-Climber ability. Razor Weasel, ahoy! The said, she won't try to continue riding Formless Airlines beyond the exit.
-[X] Telepathically warn Antonio that a flying monster might be preparing to exit the rock in a hurry and that he and all of our ranged assets should be ready to shoot at it if necessary and to try to get our spearmen and net-users into position to attack it before it can reach the sky.