Giant Donkey Kong
Giant DK first appeared as a non-playable character in Stage 6 of Super Smash Bros.' 1P Game. Giant DK has a large amount of knockback resistance, while his own attacks have increased knockback capable of KOing opponents more easily on top of having increased range due to his size, making him a formidable opponent; however, the player is given two regular-sized AI partners to help out. On higher difficulties, Giant DK behaves more similarly to a level 9 CPU while the player's partners are lower in level. It is possible to exploit Giant DK's AI, making him walk back and forth on the top platform, similar to Metal Mario along with his size making him a larger target to attacks. However, it is harder due to AI partners jumping into him or attacking him which will often interfere with his pattern.
It is possible to play as Giant DK using a debug menu code. Unlike the other unique boss, Metal Mario, Giant DK is considered to be better than his unchanged counterpart due to his greater jab range. He is, however, prone to being chain grabbed, such as by Captain Falcon or Pikachu. Despite being his own unique, separate character, he has the exact same head icon as Donkey Kong.
In Melee, Giant DK is essentially regular Donkey Kong with a permanent Super Mushroom upgrade (and can thus be temporarily playable that way or played permanently using Action Replay's Auto-Mushroom cheat). Giant DK appears at the end of the Stage 2 of Adventure Mode, after defeating two tiny Donkey Kongs. Giant DK is also very exploitable; by standing perfectly still or moving slightly towards the edge, depending on character, it is possible to bait him into using an f-air or n-air and falling into the water, resulting in a free win. This is much more likely on higher difficulties due to the more aggressive AI, and is a common speedrunning tactic for this stage. Additionally, in Classic Mode, like all giant characters, Giant DK has a chance of appearing on Stage 5 as a random giant opponent.
Giant DK appears controlled by the player in Event 2: Lord of the Jungle.
Additionally, Event 25: Gargantuans features an immensely large Donkey Kong (over twice as large as the normal Super Mushroom DK) as an opponent, while the player is a Giant Bowser, with a super tiny Mario and Peach also present.
Giant DK returns in Brawl in a similar fashion as in Melee, as a regular Donkey Kong permanently equipped with a Super Mushroom. Giant DK appears in four event matches: in Event 9: The Monster Beneath the Earth, if the player can't KO the two Diddy Kongs in time, they must fight Giant DK; in Event 22: Monkeys Unite, Giant DK appears as Diddy Kong's ally to defeat Sheik and Lucario; in Event 27: Three-Beast Carnage, Giant DK returns with Giant Bowser and Giant Charizard, attacking New Pork City; finally, in Co-Op Event 14: The Dark Guardians, Ganondorf and Wolf must defeat Giant Charizard and Giant DK, again on New Pork City. If counting both events and co-op events in Brawl, the aforementioned events are Giant DK's only appearances in Brawl.
In spirit battles
The closest analogue to Giant Donkey Kong in the Donkey Kong series is the final boss battle of Donkey Kong for Game Boy, where the title character used Super Mushrooms to become much larger and fought Mario atop the Tower that comprised World 9. In this appearance, however, Giant Donkey Kong was significantly larger relative to Mario than his depiction in Smash.
Alternatively, Giant Donkey Kong's size may simply be a reference to one of Donkey Kong's inspirations, King Kong.