ToME: the Tales of Maj'Eyal

Here are some bugs I've found with possessor's assume form talent:
Assuming the form of a void elemental does not allow you to breath in the void (you can still walk on the void tile but it quickly empties the characters air supply).

Same issue happens with the mana worm when after walking onto a space/void tile it drops to 66 air and a turn later 22 air (costing ~44 air lost per tile as if the character was stuck in a sandworm tunnel wall)

Similarly when possessing a xaren it doesn't allow you to breath while going through walls.

have you considered that maybe this is because permanent wall walking is completely and utterly overpowered rather than a bug?

I wouldn't say too overpowered, turns out xarens can only walk through specific types of wall, but I can see where that instance would be considered as such. I only mentioned it because it was similar in nature to the op's examples.