It's a cheat put into the game to up your pokemon's levels or something. I know that one your pokemon go up a level after 136, it's automatically at lv. 100. I don't think you're supposed to KEEP the missingno because it will screw your game up, but it's a cheat, that's all, that everyone knows about/should know about.
The stats don't appear because it's not a pokemon *i don't think* and i don't think you can use it.