One thing that could kinda work could be cards that let you get more than 10 copies of a specific Action card.
A really cool one could be adding "status effects" to cards, like poisoning, freezing or whatever:
Poisoner - Action Attack - 5c
+1 coin
+1 Buy
Every other player reveals cards from their Deck until they reveal an Action or Treasure card. That card gets the Poisoned type.
Discard all the revealed cards.
(when you play a poisoned card, you first gain a Curse)
Ice queen - Action - 4c
You may choose an Action card from your hand. Play it three times, and then it gets the Frozen type.
(cards with the frozen type won't have any effect the next time they are played, and then they lose the Frozen type)
Entropy Knight - Action Attack - 4c
Every other player reveals the top two cards of their deck, chooses a revealed Action card to gain the Whatever type, and then discards all the revealed cards.
(When you play cards with the Whatever type, there is a 50% chance of their effect being "+1 Card +1 Action" instead of their expected effect.)