Basically the type is Bird and Normal,
The moveset is usually Water Gun x2 and Sky Attack,
The level can be 0 to 255 when encountered,
Yes you can catch it.
The effects when encountered:
- You're item pack's sixth slot item is added with 128 more of that, perfect with master balls and rare candies
- It looks like a glitchy backwards L
- It screws up the hall of fame (in my opinion, it looks funny)
- Missingno. when used in battle scrambles the sprites (can be fixed by viewing pokedex entry)
- In Yellow, when caught makes player sprites walk around the screen.
Note: Missingno. is harmless, and won't do anything terrible to your game.
Hope this helps!