If you could make a new class for p99

[Polixenes]

My new class: Demonic Possessor (ok it needs a catchier name)

Can take direct take possession of a mob, so a charm-like function, except that the player takes control of the creature like in Project M.

Whilst in Possession of the mob, the PC's body is helpless with severe AC/resist/dodge/parry nerfage to basically make it very risky process in the presence of adds.

If the Possessed mob dies (leaving no corpse) the player returns to his own body. The duration is variable and the spell could end before going full length. Perhaps mana is expended over time in maintenance of the spell, and the amount of mana expended depends on mob level.

Spell breakage would come with a heal on the mob to its pre-possessed state, and a no-fail memblur just so the PC is not ganked instantly upon breakage, that way you don't need to give the class enchanter tools like stun/mez/blur.

Allow the PC to summon pets which are instantly possessed, for those occasions when you are fighting things that are immune to possession.

Available to Dark Elves, Humans, Gnomes, Erudites, Iksars. If we are inventing a new class lets go the whole hog and allow evil High Elves, and give it to them too.