From the Super Mario Wiki
A Cloaking Device is an item in the game Perfect Dark. It is also used as a helpful item in Super Smash Bros. Melee. If a player picks it up, it turns them almost completely invisible for a short amount of time, although they sometimes flashes back into visibility for a split-second. The player has to be careful because they can lose track of their own invisible character.
There is also a special Invisible Melee mode, in which all players have on unlimited-time Cloaking Devices, until the end of the match or matches. However, players can take damage while invisible in that game mode.
In the Event Match Slippy's Invention, the player has to defeat Fox McCloud and Falco Lombardi, who both have on permanent Cloaking Devices, but can still be damaged. The Cloaking Device used by the pair was invented by Slippy Toad.
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