Quote of what's been said before on PAO
#349 megaPAO is the most misunderstood spell in the game (and with good reason. It's not well written). Here is what it can actually do:
It functions as the spell Greater Polymorph (which itself functions as either: animal or magical beast as Beast Shape IV, elemental as Elemental Body III, humanoid as Alter Self, plant as Plant Shape II, dragon as Form of the Dragon I; Note that this means PAO cannot do aberrations, constructs, fey, monstrous humanoid, oozes, outsiders other than elementals, undead, or vermin), with the following exceptions:
1)The duration works differently, as shown in the tables (potentially being permanent)
2)It can turn creatures into objects, using the rules listed in the spell
3)It can turn objects into creatures (while it says it can do this, the mechanics for doing so are not fully explained, due to how polymorph changed between 3.5 and PF. For instance, what is the objects HD? BAB? base saves? etc.)
4)Finally, PAO can be used to mimic one of the following spells instead of the above uses: baleful polymorph, greater polymorph, flesh to stone, stone to flesh, transmute mud to rock, transmute metal to wood, or transmute rock to mud
Note that when polymorphing into a creature, you do not gain that creature's stats or special abilities. Instead, you gain bonuses to your own ability scores as appropriate for the polymorph spell (Beast Shape IV for animals, etc.), and any special abilities that polymorph spell lists, as well as all natural weapons.