From the Super Mario Wiki
Coin Coffers are enemies that first debut in Super Mario 3D Land. They have small eyes on top of their head, are round, have a light green color, and slightly resembles a frog's head, as well as a purse. Their name is a pun on "coin cougher", with "coffer" being another name for a container used for storing money or valuables.
Super Mario 3D Land
Coin Coffers react similar to the Moneybags as they attempt to run away from the player. In Super Mario 3D Land, they contain ten coins. Hitting a Coin Coffer in any way causes it to drop a coin, dazing it, and after five hits, it spits out the rest of the coins it contains before it is defeated. Ground Pounding one causes it to spit out all of its coins before being defeated. When hit by Mario under the effects of a Star, its ten coins are dropped in a ring shape. Coin Coffers first appear in World 2-3, though one can be found hidden in a rock in World 2-1. Some Coin Coffers are hidden under rocks and grass.
New Super Mario Bros. 2
They also appear in New Super Mario Bros. 2 similar to how they did in Super Mario 3D Land. They appear sometimes after activating a Red Coin Ring too, dropping eight Red Coins as it bounces. If Mario defeats it before it can release all the Red Coins, they will all be dropped. They only appear in World Star-1 and World Star-7, as well as several DLC courses.
Super Mario 3D World
Coin Coffers also appear in Super Mario 3D World. They act the same as how they do in Super Mario 3D Land. However, they are now invisible and hide in certain hidden areas of levels. They can be made slightly visible by touching them on the GamePad, and jumping on them will fully reveal them.
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