While I knew of the polymorph--> alternate form errata years ago, I never realised its impact on the monsters in the MM. Only recently was it brought to my attention that for a phasm, replacing polymorph with alternate form meant that it was free to take on any form of up to large size, regardless of type and HD.
I am in the midst of adapting a few side-treks to 3.5 to slot into the City of Spider Queen module, and one from an old issue of dungeon involves an ambush comprising of a mimic, medusa and phasm. The forms suggested didn't seem very inspiring (troll/arrowhawk) against a 10th lv party. So I am wondering what more powerful forms the phasm can assume?
At first though, pit fiend? Solar? Am I overlooking anything? This seems way out of line for a cr7 monster, though its unchanged hp of 97 seems to be its biggest weakness.