Cards for Serpentis

To expand a bit, I believe there is two kind of deck that could use corruption card.

The first one would be a corrupting deck proper that try to get a minion advantage via corruption counter. For now, the two problem of that kind of deck are :
1 - they are slow as hell to corrupt vampires. You get 1 corruption counter per action in almost every case, so 11 actions for an Inner Circle. There is some way to get them faster : Weight the Heart on a corrupting action (max 2 vampires on your crypt can play it and they are 8+ cap), Cagliostro with his ability and Venenation (and you need your prey blocking you), and Revelation of Wrath (depend on your opponent).
2 - once they have spent 8+ action corrupting a vampire, they need to actually oust their prey, which require entirely different cards. it's the same problem as combat deck, except you need even more action than combat (but in all fairness, they are way harder to stop)

Given that, I would give them something like that to work a bit better :

The Rotten Apple
Action/Action Modifier
Requires Serpentis
Cost 2 blood.
Only one The Rotten Apple can be played per turn.
Action modifier. When you burn corruption counter to take control of a vampire, his controller burn 1 pool per corruption counter burned
Action. Put 2 corruption counter on target vampire who received a corruption counter this turn.

(notice that Form of Corruption don't use Corruption counter)

The inferior level make the deck actually oust his prey. Given the rate of corrupting, it's not that powerful : with 8 action, you can corrupt an Inner Circle and do 11 pool damage, while a lasombra can do 11 pool damage in 2 bleed, dunk the inner circle in 3-4 rush, and steal it via Graverobbing in one action.

The superior level make the rate of corruption significantly faster, but is limited to one per turn and require another source of corruption. Also, you cannot use it and the inferior level the same turn.

The other kind of deck who could try to use corrupting action is a deck who does not try too hard to get new minion, but use Revelation of Desire or vampire special to benefit of thoses. The main problem is that losing an action to activate those is too expensive by a fair margin. One action to get +3 bleed or to get 3/4 vote ain't cutting it.

For thoses decks, I would add a card like that :

Revelation of frustration
Action Modifier
Requires Serpentis

Play when a vampire is trying to block. If the action is successful and this vampire doesn't have corruption counter, add one corruption counter on him.
As above, and add +1 stealth.

The inferior level allow you a cheap way to get one corruption counter (but not more than one), so Revelation of Desire look much more playable.
The superior level help to make your action succeed, so you have less moving part with big serpentis vampire.