This contest involves a mechanic I am developing called Sneak. This is the same as the Jackpot ability I wrote about a while ago, but I'm changing its name in order to better fit with a new theme for a new set I want to make.
Sneak is an ability that you can use any time on your turn other than clean-up, but only once per turn. It can be used before resolving beginning-of-turn effects, in the Night phase, or any time in between. When a card has the Sneak type, it means you can play it using its Sneak ability, indicated by the text "Sneak:", instead of its regular ability. So, if a card has both the Sneak and Action types, it means that once per turn, you're allowed to play the card at any time using its Sneak ability, but then any other plays of the card (or copies of it) have to be in the Action phase, using its Action ability. The Sneak type is indicated by a dark blue color, and Sneak - Action cards should have both colors.
Some examples (I'll make pictures later):
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Swordsmith
Action - Sneak - $5
+3 Cards
Sneak: +3 Cards, then put 3 cards from your hand onto your deck in any order.
It's just a plain draw card when you use the action ability, but the Sneak has lots of uses, depending on when you use it.
Action phase: It can possibly save you from a dud turn.
Buy phase: You can draw Treasures and then also top deck dead Action cards.
Night phase: You can draw and top deck cards you just bought.
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Scheming Court
Action - Sneak - $5
You may play an Action card from your hand twice.
Sneak: Replay a card you have in play twice.
Again, a card where the Action part is already an official card (Throne Room), but the Sneak is a bonus. It's basically a once per turn King's Court, but it can also work on Treasure and Night cards.
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Machine Shop
Action - Sneak - $4
+$1
Cards cost $1 less this turn.
Sneak: +2 Buys. Gain a card to your hand costing up to $3.
The Sneak is less useful here when used in the Buy or Night phases, but the gained card can be better if you've already played one or more Machine Shops. Also note that the buying power is overall more limited compared with Bridge because only the Sneak gives you +Buys.
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Hidden Village
Action - Sneak - $4
+1 Card
+2 Actions
Sneak: +1 Card. Put a card you have in play on your deck.
Lets you replay a card if you have the Actions left over for it, or Scheme a card in the Buy or Night phases. The fact that it's a Sneak ability helps to avoid infinite loops.
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This is an example of a pure Sneak type (or close to pure, at least):
Secret Mission
Sneak - Duration - $5
Sneak: Take another turn after this one where you can only play Action cards.
This is a redo of the Voyage card I made. Originally, it was a Night card that forced you to end your Night phase so you couldn't play another one. I realized that with the Sneak mechanic I could drop that part. Also, instead of an explicit Action-only restriction it had you discard your hand at the end of your Action phase, but it was pointed out that Village Green could still give you infinite turns. Making Action-only explicit is simpler anyway. I also had to choose a different name obviously!
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Lastly, here's a card that uses the Sneak ability without actually having the Sneak type:
Jeweller
Action - Treasure - $5
If this is your Action phase, +2 Cards. Otherwise, +$1 and +1 Buy. Either way, you may use your Sneak to return this to your hand.
It's not a Sneak type, so it can only ever be played in the Action or Buy phases. But, once per turn, you can return it to your hand after playing it. I made it an Action - Treasure so that returning it to your hand is still useful even if there are no Villages on the board.
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Things to keep in mind overall are all the different phases that the Sneak can be used in, as well as the fact that it allows things that would break the game if they could be used more than once per turn.
Also, I'd like some feedback on how well you think this mechanic works overall. My main concern is boards with more than one Sneak card on them. It seems possible that, because of the once per turn restriction, one of the Sneak cards would end up with only its plain ability being used. I thought about making the restriction instead "once per turn per pile", but that seems too complicated. Does anyone have any other ideas?