Kind of conventional but whatever.
King's Signature
Action-Treasure-Victory
Cost: $8
If it's your Action phase, play an Action card from your hand twice.
If it's your Buy phase, play a Treasure card from your hand twice.
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2 VP
How about King Midas's Court 8 (8 debt)
If it's your Action phase, play an Action card from your hand three times or Turn all your coins in hand into gold during action phase.
If it's your Buy phase Can transform only 3 coins to golds before buying cards.
Just imagine this in a Gladiator/Fortune game. Or it could just flip the Mountebank into a gold machine, turning lead into gold. Especially ridiculous b/c you could gain it in lieu of first province. Maybe even Have this underneath the KC pile, so that the first 5 are Kc's and last 5 are King Midas Courts.
First, this seems kind of completely different.
Second, for Midas, I think it should be a duration that turns an Action card into a Gold each turn (or reveal that you cannot and gain a Curse)
Strictly for theme reasons, it should play itself compulsively once you've played it at all. The Actions requirement is both for theme and to make the penalty more troublesome to deal with. On some boards it might not be a problem, but you need a lot of start-of-turn or end-of-turn deck/hand control, and you're always gaining more junk to sort through, and is it worth it? Maybe?