That could be an interesting idea:
Troupe
Types: Action
Cost: $3
+1 Card
+1 Action
This card is considered to have all types. You can still play it only as an Action card.
Doesn't do anything by itself, but comboes with a lot of stuff?
I tried to word it in such a way that you could choose which type it has whenever you want, but then either it has no type while it is in the supply (no cute Mine Copper into Troupe trick, etc.), or other players get to choose while they are attacking you.