The thing about promo cards is that they are designed as promotional tools. I don't know the history on the existing promos, but wasn't Stash published to commemorate Dominion winning the SdJ? And Governor and Walled Village for anniversaries of Puerto Rico and Carcassonne?
What is happening this year that would prompt a promo? My guess is that this will be the online-only promo intended to promote Goko.
Goko
Action - $3
+2 Coins. Each player trashes the top card of their deck, representing their favorite online gaming platform, and gains a sucky card of supposedly equal value that you choose.
Hmm…
Goko
Action - $4
Trash a card costing $0 from your hand. If you do, the player to your left chooses a card in the supply costing $3 or more. Gain that.
More like:
GokoAction - $4
Each Player reveals the top two cards of their deck. If the first card costs 5 or more, that player must leave the table for at least as many minutes as the cost in coins of the second card. (The player may get a drink, preferably something strong). Each player may trash a card. If a player that is not the active player trashes a card costing more than the most expensive card the player revealed, the player must play the remainder of their turn with their hand facing away from them. Their turn does not end if they attempt to play a card that cannot be played (for example, Estate) but the buy phase will be triggered if they play a treasure.
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Setup Instructions:
If you do not have Goko Salvager, you must hop around your house/apartment/building visiting each occupied room in the house/apartment/building you are playing in at least once and possibly twice before you can start a game. Goko is a required part of the supply. You may not play dominion without it. It does not take up a kingdom slot however, add it to the game in the same manner you add potions/platinums/colonies.