Ok, I have an incomplete idea for Werewolf. It should probably be an Action-Duration-Attack, performing its attack the turn after it is played (gotta wait for that full moon). I also figured it should Curse you when you gain it, but then the attack needs to be appropriately strong. It should also be an agile creature, so cantrip it is?
idk, here's one version, I doubt that it would be stable enough for real games:
Werewolf
Cost: 5
+1 card
+1 action
At the beginning of your next turn, each other player reveals cards from the top of their deck until they reveal a card costing between 3 and 6. Trash that card.
When you gain this card, gain a Curse.