PokeMan's version (2000)
YochiThMaster333's second version (2017)
Pikachu is an Electric-type Pokémon from the Pokémon series who serves as the series' official mascot. It has appeared as a playable character in every game of the Super Smash Bros. series as well as being playable in both its regular form and in its Pikachu Libre cosplay outfit in Pokkén Tournament. It evolves from Pichu and evolves into Raichu. It appears at #025 in both the Kanto and National Pokédexes.
Pikachu is a small, chubby, rodent-like Pokémon and the first recorded species with the distinctive electric cheek pouches present on other small, rodent-like Electric-types such as Plusle, Minun and Pachirisu. From these pouches, Pikachu can discharge concentrated bolts of electricity at any chosen target with high precision. Pikachu are normally very docile and easily approachable, but will still travel in packs for the protection and welfare of each other.
In M.U.G.E.N, Pikachu has been made by many authors due to its popularity, being a character with versions spanning from as early as the year 2000 to as recently as 2017; some of the older versions do not function in more recent versions of M.U.G.E.N as a result of being coded in the DOS M.U.G.E.N era, where compilers were less effective at picking up errors, though they have been edited by other creators to fix such compatibility issues.
The very first known Pikachu character, which is better known by the edit that was made eight years later, is very basic. Using only two buttons, it lacks any real form of comboing, but to make up for it, it is quite powerful. It shares similarities with the Bulbasaur, Charmander and Squirtle characters made by an unknown creator.
The colour issues that make this old version of Pikachu appear mostly grayscale are the least of its worries, as this relic from the DOS M.U.G.E.N era fails to function properly in WinMUGEN or later because of several errors in its coding, so don't expect it to be fighting again without first taking it to the nearest Fighter Factory.
Another DOS M.U.G.E.N Pikachu character, Milano's PIKACHU will not function in WinMUGEN and newer due to multiple errors; this is to be expected, as it is a spriteswap of the original Kung Fu Man, a character that also fails to function outside of DOS M.U.G.E.N. The majority of the character is exactly the same as Kung Fu Man, though it disappears during its Normal Attacks.
Chaos Team's version
Despite being referred to as "Super Smash Bros Melee Pikachu" by both its creator and its internal name, it plays very little like Super Smash Bros. Melee's incarnation of Pikachu, bearing resemblance only in its attack animations; not even its sound effects are from Melee, or any Super Smash Bros. game for that matter.
The only known hi-res Pikachu character, this version uses custom sprites and originates from a M.U.G.E.N-based full game known as Pokemon GT; the character doesn't translate well from said source game, however, so while it is a direct port, it can only attack other characters from Pokemon GT and is unable to deal damage to regular characters.
The creator states that this Pikachu is Super Smash Bros. Brawl-styled, though this couldn't be further from the truth, with the only essence of such a game being its sprites. The character's moveset is very limited, with just nine moves at its disposal across only two buttons; four of these attacks become infinites when timed correctly and cover the entire width of the screen.
MUGENX's pika plays very closely to the Super Smash Bros. incarnation, to the point where it becomes very overpowered; all pika has to do to defeat the opponent is knock them far enough to the left, right, or top parts of the screen, where they will get "K.O.'d"; doing this three times causes their Life to drop to 0, delivering an actual K.O.
Even if it doesn't have much in terms of a movepool, it's hard to ignore how undeniably spammy this Pikachu is, catering more to button-mashers with certain moves that can only be activated though repeated presses of specific buttons. Perhaps this character should have been called "Spamachu".
HCL's Pikachu holds true to Pikachu's weak but agile and combo-heavy philosophy, being able to zip across the stage at high speeds and perform devastating aerial raves off a launcher, complete with multiple mid-air jumps to really keep the pressure going. Its A.I. is no slouch either, making the most out of its comboability and mobility, though it often forgoes blocking and gets beaten quickly as a result.
Bruno_SS' first version
Very weak and with a limited moveset, this Pikachu isn't going to be winning many fights. Though it is able to chain its weak attacks together from light to heavy, the average damage output from doing so is about the same as a standard character's light punch. Its stronger attacks require Power, but are significantly more powerful than its weak attacks.
Plagued with problems right from the get-go, this Pikachu is a literal spriteswap of Kung Fu Man, with most of the hitboxes and code left intact. Due to erroneous code, some of Pikachu's attacks fail to make contact, while other attacks fail to activate at all. If a Trainer were to come across this Pikachu in the wild, one can only hope they decide against catching it.
This supposed update to the original version is just as weak and just as limited in its moveset. Unlike the original, however, it is practically impossible to chain its weak attacks together, though its strongest weak attack can be an infinite if timed well enough. Ironically, one could argue that it seems less complete than the original.
They say OPchu is OP, but so are all of the characters from AxKing's Pokémon full game. Its comboability is practically non-existent outside of mashing the same buttons repeatedly, so it's no surprise that Pikachu comes packed with its own set of infinites, though while they are a little bit tricky to pull off, defeating any opponent becomes a breeze... That's not a good thing, by the way.
Though one might think this is an edit of Chaos Team's Pikachu, the base character is actually Kung Fu Man; saying that, some of Pikachu's moveset is still inspired by Super Smash Bros., such as Skull Bash, which can be charged up to do...absolutely nothing different from its uncharged counterpart. Pikachu's damage scaling is incredibly restrictive, though the character's distinct lack of comboability effectively nullifies that.
YochiThMaster333's first version
Using the same sprites as Chaos Team's "Melee"-styled Pikachu, this version aims to be somewhat accurate to Pikachu's Super Smash Flash incarnation, though the creator didn't quite manage to get tilts working, hence why Smash Attacks are their own buttons. They say lightning never strikes the same place twice and that's probably because it'd cause infinites if it did, or at least, that's what this Pikachu will have you believe.
Gladiacloud & Dylanius9000's version
A lot of Pikachu characters boast movesets inspired by the electric mouse's appearance in the Super Smash Bros. series, and while this version is no exception, it also throws some of Pikachu's techniques from Pokkén into the mix. Pikachu is very agile in both its movement and attacks, and can hit surprisingly hard for something so little, but its shocking 700 Life stat can potentially dampen the voltage of this live wire.
Bootlegged and ready to roll, GodzillaFightn's 'Pikachu' drops into battle kicking and screaming, though its team of fellow bootlegs are always remaining close by to help it out. 'Pikachu' is purposefully clunky, featuring weighted jumps, the ability to run up walls and stay there, and slow attacks that typically have long cooldown times before they can be used again, while also being able to K.O. itself very easily by overcharging its Rocket attack.