guys you can encounter missigno in Pokemon Fire Red/Leaf Green
it looks like a "B" with a slash "/" B/ is what it looks like except it is a little more squigly.
it is called "FG33" it is number .000 on the pokedex, i tried to train it and it evolved into a Trapinch with Hydro Cannon, Volttackle, Waterfall, and Vine Whip. but since it evolved i have not been able to get it to go any higher level. i have tried a Rare Candy on it and it still will not grow a level, it is at level 7 with *turns on gameboy*
200 HP
200 ATK
200 DEF
200 SP. ATK
200 SP. DEF
200 SPD
and it evolved with the nickname "DEATH"
i encountered "FG33" aka "DEATH" when i went into cerulean cave after i beat the e4, i was surfing to Mewtwo when the "missigno" came up after a random battle started.
i don't know what i did for it to come up, does anyone here know?