Yeah, you can still start a new game, as far as I know, but don't bother with catching that glitchy Pokemon.
...It's base stats and overall usage are pretty average.
It has a massive base 136 Attack Stat, but with a Mediocre Base 0 Defense, it won't be lasting very long in battle. And with a mere Base 36 Speed, it doesn't make a good sweeper.
Not to mention with it's normal/999GlItCh typing, it leaves it vulnerable to fighting attacks, and packs no resistances.
Finally, it comes in four different forms, and none of these forms differ much, so it's not much more than a gimmick.
...Yes, I just spent this whole answer making a mockery of MissingNO. But yeah, in summary, don't catch him. It just screws up your game.