It must be sometimes terminal and sometimes not. This could include playing another card, or conditionally giving +actions, etc.
It must be able to trash a card (one of yours).
It must be able to gain a card.
Keeping in mind that it will also have a reaction that reacts to anyone gaining a card (with conditions on the gained card); the card must be strong enough that it should cost $5 or more.
Some Card - Action / Reaction - $5
+1<VP>
Trash a card from your hand.
+<VP> equal to half the number of differently named cards in the trash, rounded down. <-- This wording is a bit awkward
You may spend any number of <VP>. +1 Action per <VP> spent this way.
When another player gains a card, you may discard this.
If you do, +<VP> equal to half its cost in Coins, rounded down and your opponent may trash a card from his hand.
It might be trying to do a bit too much, but I'm open to tweaks.