Through the hallucinations, would it be possible to tell the layout of the cave/the placement of the people in it? Like, if they're all in front of the thing, would it be feasible to cause a cave-in just in the back, where the pool is, with a minimum risk of casualties? This would be done via magic, sending energy through the cave wall itself to cause a collapse rather than directly manipulating anything (basically, he's not an earthbender, he can just generate his own explosives).

Would this be helped at all by holding Shepard's creepy possessed pacdisk?