Pichu sucks in Smash. Almost all of his attacks hurt him in one way or another. He is even considered one of the worst characters to use in Melee (the others being Bowser and Kirby.).
Not too many Gen 2 Pokémon are horrible even Wooper but I'm eliminating Wooper this round for it being too common in the Mystery Dungeon games I've played and it being easy to defeat with Grass type moves in those games, especially the former (but both remind me of the hell of boringness gameplay is in the PMD games)
Chikorita
Bayleef
Meganium
Cyndaquil
Quilava
Typhlosion
Totodile
Croconaw
Feraligatr
Sentret
Furret
Hoothoot
Noctowl
Ledyba
Ledian
Spinarak
Ariados
Crobat
Chinchou
Lanturn
Cleffa
Igglybuff
Togepi
Togetic
Natu
Xatu
Mareep
Flaaffy
Ampharos
Bellossom
Marill
Azumarill
Sudowoodo
Politoed
Skiploom
Jumpluff
Aipom
Sunkern
Sunflora
Yanma Wooper
Quagsire
Espeon
Umbreon
Murkrow
Slowking
Misdreavus
Wobbuffet
Girafarig
Pineco
Forretress
Gligar
Steelix
Snubbull
Granbull
Qwilfish
Scizor
Shuckle
Heracross
Sneasel
Teddiursa
Ursaring
Slugma
Magcargo
Swinub
Piloswine
Corsola
Remoraid
Octillery
Mantine
Skarmory
Houndour
Houndoom
Kingdra
Phanpy
Donphan
Porygon2
Smeargle
Tyrogue
Hitmontop
Elekid
Magby
Miltank
Blissey
Raikou
Entei
Suicune
Larvitar
Pupitar
Tyranitar
Lugia
Ho-Oh
Celebi
Whitney's Miltank is quite tough to beat. If you don't have a Fighting Type that is the same gender as her, you're going to get beaten easily, especially if you have Fire or Flying Type Pokemon. Not even Ghosts can win, as her ability in the remakes is scrappy, which allows her to attack Ghosts without having someone else use Foresight, Odour Sleuth, or Miracle Eye.