It's a nice idea, but I feel like the $3 cost makes it a bit too easy to game the pile.
I mean, if the purpose of this card is to mitigate the problems of losing an important split, this will often just make the problem worse.
Especially given that you aren't going to want to buy it for $3 except when a pile is just about to empty, because who the hell wants a dead card for $3?
Basically, I'm about to buy the last of whatever card we're competing for and win the split, but if I've got an extra $3 and a +buy I can buy an Actor as my first buy and then buy the last whatever.
Now instead of being ahead of the split 6-4, I'm ahead 7-4 and, assuming this key card costs at least $4, I got this hefty advantage at a bargain price.
Why not just have the price be $? so that the card is effectively ungainable until the first pile is empty.
That also means that if the first pile to empty is Province, the player emptying it needs $16 and a +buy to steal the win on an even split, rather than just $11.
It is intended that you can go gambling by buying dead $3 Actors. This can be quite a good investment if it will turn into a Grand Market or a Hunting Party or a half-Province. It can be a bummer if Curses run out first though.
If you happen to get a cheap [whatever] right before you get the last real [whatever], I don't think this is bad. Maybe it can even create a sort of "penultimate Grand Market rule". Why not?
Might be cleaner to limit it to "non-victory card", or even "action card".
Sure, this would be much cleaner. I thought about this as well, but I generally prefer the crazy versions because that sounds more fun.
In my mind, this card had had Band of Misfits' wording originally:
If an Action pile in the supply is empty, play this as it were a card from that pile. This is that card until it leaves play.
Otherwise, +$2 (or something).
Then I thought, why not copy Victory piles? Wait, 6 VP for $3 is a bit too much in Province games. So half the score it is.
Maybe Colonies are an issue. But again, players can balance that out because they will likely buy out another pile first if a player goes heavy into Actors.
Also, i wanted the gambling.
Rules clarifiation: If a mixed pile gets empty first (Ruins or Knights), there is no specific card to imitate for Actor, so it fails to imitate anything.