Rest (ねむる, Nemuru, or Sleep) (referred to as Sleep on the original SSB's website) is Jigglypuff's down special move in all three Smash games. Jigglypuff turns toward the camera and falls asleep for about 5 seconds. Before Jigglypuff falls asleep, any opponent in contact with it is instantly hit, with a Ping sound being heard. This attack is known for having high knockback, no startup lag, very small range, and a long vulnerability period. However, Jigglypuff gains invincibility for 20 frames, approximately the time it takes to close its eyes.
In Super Smash Bros. and Super Smash Bros. Melee, Rest was a powerful move that dealt high damage and knockback. In Melee, it could be combo'd into using some of Jigglypuff's moves, such as up throw or up aerial, and it can KO reliably at as low as 25%. However, during the transition from Melee to Super Smash Bros. Brawl, it was heavily nerfed (with its KO power being drastically reduced so that it starts KOing reliably at 75%).
 Changes from SSB to Melee
 Changes from Melee to Brawl
The Smash Bros. version of Rest is completely different from the Pokémon version. In Pokémon, Rest is a status Psychic-type move introduced in Generation I, that does not do damage to opponents; instead, it puts the user to sleep for two turns in exchange for the user gaining all of its HP back to its maximum and healing any status ailments, but this could also leave the user open for attacks or have their opponent do something else useful for themselves while it sleeps. In the Smash Bros. series, Rest can't be used to heal damage, and Jigglypuf falls asleep for some seconds when using the move, leaving it vulnerable to attacks but dealing damage if used near a foe. In Snake's Codec Conversation about Jigglypuff, Colonel says this is because "there's a huge buildup of energy in its center of gravity". This is an example of the Smash producers changing the function of moves to suit the games; other examples include Withdraw and Double Team.
In every Pokémon generation, Jigglypuff can learn Rest by leveling up, being one of the few Pokémon that can do so. Also, every Pokémon that is capable of learning moves via Technical Machines (all Pokémon, except "useless" ones like Magikarp) can learn Rest via TM44.