To get into the dimension the player has to activate a chain of events. Catch a Bulbasaur, get a fossil Aerodactyl and revive it, mine gold ore and smelt it then make a pokeball. After these are done, sleep.
In the dimension you fight MISSINGNO. instantly and he could be invincible! The player could only use a master ball on him or throw the match. If he's caught he would have these stats -
MISSINGNO.
LV.50
HP 125
ATK 200
DEF 25
SPD 35
Unpredictable Nature
Basically a normal MISSINGNO.'s GEN1 stats (But not the level) It would have it's own nature which ups it's HP.