1. People think Togepy evolves into Chansey. Well, I have proof that Togepy doesn't, because Togepy evolves into Togechikko!
 

2.You can't get Mew on a gameboy for now.  I think you can get it in the gold/silver versions.  But for now you you have to trade with someone who has a Gameshark of use your own Gameshark.

3. It is impossible to get Pokemon whose number is higher than 151 on pokemon blue/red/yellow. You can't because the Pokemon's data wasn't made in the game. You can only get them on the gold/silver versions.