I made a topic a while back on this, but I thought I'd make a new topic for the final versions, with a new mechanic
There are 6 Trinkets, and only one copy of each. At the start of games using them, you randomly replace ONE copper with a Trinket.
All of them are "better" than Copper, and the initial advantage you get may play into the kind of strategy you ultimately pursue.
Without further ado, the cards:
Rare Coin
Treasure/Trinket - $4
Worth $1
Toy Bridge (credit to dondon151)
Treasure/Trinket - $0
Worth $0
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While this is in play, cards cost $1 less, to a minimum cost of $0
Key to the City
Treasure/Trinket - $0
Worth $1
+$1 for each empty supply pile
Bell
Action/Trinket - $0
+2 Actions
+$1
Dagger
Treasure/Reaction/Trinket - $0
Worth $1
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When another player plays an Attack, you may trash this. If you do, you are unaffected by that Attack.
Trinket Box
Treasure/Victory/Trinket - $0
Worth 1VP for every 2 treasures other than Copper, Silver and Gold in your deck (rounded down)
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Worth $1
Note that there are many games in which a particular Trinket is useless. I doubt that there will be many boards in which only one is useful however, and none of them are going to win games on their own.
EDIT: Changed the rules on how many you get, and a few other minor changes.