One-shots, eh? Here's my take on it;
Schrödinger's Cat : Action : $4
+2 Cards
You may trash this for
+1 Card and +1 Action.
-
While in the trash, this is also in the Supply,
(but not in it's pile).
Originally, this had an additional +$1 along with the +2 Cards, but it was too annoying to count during playtesting. This is like Experiment, but it never really runs out, and it doesn't have to be a one-shot.
Some clarification about what "While in the trash, this is also in the Supply" means -
1. The Schrödinger's Cat pile doesn't count the cards in the trash. (So, the pile can still run out, even if you can still buy some from the trash.)
2. Schrödinger's Cats that are in the trash are still in the supply, just in the trash pile. That means they can be bought and gained as one normally would, just from the trash instead. (eg, Workshop could gain a Cat from the Trash.)
Sorry the art and name aren't so "dominion-y" - I didn't really have any dominion ideas to go with this mechanic beyond "undead".
Cool contest! I look forward to more submissions.