Crazy Hand (クレイジーハンド, Crazy Hand) is Master Hand's left hand counterpart first appearing in Super Smash Bros. Melee. While Master Hand's movements are very smooth and calm, Crazy Hand moves in erratic ways.
Crazy Hand's basic appearance is exactly the same as Master Hand's (apart from being a left hand), but he is more chaotic in general, befitting his impulsive and destructive nature. When preparing for an attack, Crazy Hand's movements are also different. When joined with Master Hand, they can perform several cooperative attacks. He, like Master Hand, is always fought on a version of Final Destination.
While Crazy Hand as a character is unique to the Smash series, his attacks (as well as Master Hand's) are very similar to Wham Bam Rock's attacks in Kirby Super Star. Wham Bam Rock performs a move that involves putting its hand over the player and making rocks fall. Crazy Hand does a move that is very similar, except that Crazy Hand's rocks explode with darkness. Both Wham Bam Rock and Master and Crazy Hand perform a move that involves "walking" across the stage to flick the player. They both will also try to grab on to the player and cause damage. 
Main article: Crazy Hand (SSBM)
Crazy Hand is fought in Melee when Classic Mode is cleared on Normal difficulty or higher in 5 minutes and 50 seconds or less, after Master Hand's health is reduced by half. He also appears in Event 50: Final Destination Match (referred to only as "the left", where both it and Master Hand are fought from the start.
Main article: Crazy Hand (SSBB)
Crazy Hand reprises his role at the end of Classic Mode. To fight him, the player must arrive at the final stage in 9 minutes or less with the difficulty level set to Hard or higher. However, if the player encounters him (once the criteria is met), Crazy Hand appears in the final stage right away instead of reducing Master Hand's HP by half. Both Master Hand and Crazy Hand start with the same number of HP (dependent with the difficulty chosen). He also appears as one of the many bosses in Boss Battles Mode, where this is the only time Crazy Hand is fought separately from Master Hand and can be faced without any special conditions.
Unlike every other boss in Brawl, Crazy Hand does not appear at all in The Subspace Emissary (unlike Master Hand, who appears prominently but is not fought). Despite this, his trophy, when arranging the collection by series, is listed in the "The Subspace Emissary" section. Crazy Hand is the only boss that does not have to be fought in order to unlock Boss Battles, and is the only boss in the mode to not make an appearance in the SSE.
Brawl also gives Crazy Hand a more unique, higher-pitched voice than in Melee, where his voice was rather similar to that of Master Hand.
Main article: Crazy Hand (SSB4)
Crazy Hand once again reprises his role at the end of Classic Mode. To fight Crazy Hand in Super Smash Bros. for Nintendo 3DS's Classic Mode, to the player must reach the final branch while the difficulty is set to 3.0 Intensity or higher, and then choose the black path. On Intensity 8.0 and above, the black path is the only one available, so Crazy Hand is always fought. In Super Smash Bros. for Wii U, the player will always fight Crazy Hand at the end of Classic Mode as long as the Intensity is 3.0 or higher. He can also be fought alone in Crazy Orders.
Also, once Master Hand loses a portion of his health on intensity level 6 or higher, Crazy Hand teleports out of the battle with his body rapped in a cloud of dark flames, while Master Hand's glove flails in a Crazy-hand like fashion and rips open.
Crazy Hand's trophy appears in both versions of the game.
Main article: Crazy Hand (SSBU)
Crazy Hand appears as the army led by Galeem's dark counterpart, Dharkon. He also reprises his usual role as a boss in Classic Mode. For the first time in the series, Crazy Hand has the ability to face left. In the Final Realm of the Adventure, after Galeem and Dharkon have been defeated individually, the true Crazy Hand is found near Bayonetta, perpendicular to Master Hand near Palutena.
After defeating him and freeing him of Dharkon's control Crazy Hand flies in between Galeem and Dharkon and cracks open the reality between them. Following that he helps Master Hand fully break through to the final boss where the player faces both Galeem and Dharkon.