This looks quite good. The attack part is interesting. Other players have to decide whether they block it with a Moat (if available of course) before the player plays the Treasure. So, they don't know beforehand whether they miss to gain a Gold.
This could potentially make it political, though.
If you have both a Gold and Copper in your hand, you could choose what to give to certain players based on who blocks it in multiplayer, especially in three players.
Personally, I'd get rid of the attack completely and just have, "each other player may gain a copy of it."