Evil Coin

From the Super Mario Wiki

“Be careful; when you pinch Wendy's pennies, they pinch back!”
—Mario, Hotel Mario

Two Evil Coins.

Evil Coins are enemies that have only appeared in Hotel Mario. in Wendy's Blitz Snarlton Hotel, Mario and Luigi must be careful when collecting Coins, as they may really be Evil Coins in disguise. When they are approached, Evil Coins grow eyes, two very heavy eyebrows and a smirking mouth.

While Evil Coins have not since appeared in any other game, the concept of enemies masquerading as Coins has appeared in other games. For example, to trick Mario in Super Mario Sunshine, Boos would encase Coins inside themselves and turn invisible. Like trying to collect Evil Coins, trying to collect these Coins hurt the player.