Hi, I've looked over this piece, and now I have the time for a little 
commentary.
	I do agree that everyone's dark urges seemed a little underwhelming in 
the OAV.  I guess Rumiko Takahashi was trying to tell us just how deep that 
perfect japanese housewife exterior of Kasumi's goes.
	Anyways, there's the question of who will be possesed next and how their 
unleashed darkside will manifest.  Let's see, Shampoo's prety obvious, she'd try 
to kill all her competing Fiance's, and if she stays possesed long enough she'll 
try to shove some mind controlling spice down Ranma's throat so that she can 
make him love her then reject him.  Mousse I see as sudenly wanting Revenge 
against Shampoo for rejecting him all those years, and she's likely to be in 
real trouble since he wouldn't hold back with the oni possesing him.  Ok, 
Soun... I don't know, maybe trying to engage Nabiki and Kasumi to Ranma too?
	Now though there's the title possesion, Ranma.  And while Kasumi stayed 
possesed because no one could bring themselves to hit her, if Ranma was possesed 
it'd take someone like Colougne or Happosei to hit him.  Now what sort of evil 
things would Ranma do.  Ok, geting really violent is one thing, but he'd only do 
that against a few folk like his father.  Ryouga he might beat up a bit, but 
he'd want to make sure he was conscious for when he explained to Akane how 
stupid she was for not realising P-chan's secret (With Ryouga and hot and cold 
water for visual aids).
	Beyond embarasing Akane over Ryouga/P-chan, Ranma would also torment her 
by insulting her and not letting her hit him, Kissing her then telling her that 
Shampoo kisses better, and making her eat her own cooking.
	Now on to the other fiancee's.  With Ukyo some things he could do 
include:  Telling her that he can't stand Okonomiyaki, Asking her to be the best 
man at his and Akane's weding, Treating her like she's a boy, and of course, 
kissing Akane when she's watching(He might do this for Shampoo too).  With 
Shampoo he could: Knock her out and make her think Gosunkugi defeated her, Kiss 
her then complain about how bad she is at kissing, and raid the Nekohanten magic 
food storeroom and make something for HER to eat.

	Just a few thoughts.