From the Super Mario Wiki
When characters grab this item, a clone of themselves appears. The clones keep the original characters' state (for example, Fire Mario gets a clone that also has a Fire Flower), power-ups affect all of them, and they all move identically. The clones can be used to activate certain switches and platforms. There can be up to five clones at one time. If players hit question blocks which contain Double Cherries when five doubles exist, a Coin will come out instead. The clones disintegrate if harmed, and they all disappear when the player grabs the Goal Pole, awarding 1000 points per clone. The players can also Ground Pound on other players to steal their double power.
Double Cherries also appear in Captain Toad: Treasure Tracker, acting just like they did in Super Mario 3D World.
Super Mario 3D World
Captain Toad: Treasure Tracker
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