Try catching lots of Pokemon. Train them so that they'll evolve. Trade with other versions. Buy Pokemon from the Gaming Center. These are all ways to increase your Pkedex. Good luck.
no. because no Pokemon goes over 100.
you have to battle against other Pokemon that are level 100
Yes
No, it's impossible for a legit pokémon to go over level 100.
no
No, you cant go over Lv. 100 i tried, it didn't have an effect.
That is impossible without cheats.
You can't, even with hacking.
if the game has a glitch
There is no such code for that. The game can only allow you to have Pokemon up to level 100. No Pokemon over level 100 exists.
no you can't 100 is the highest level on all Pokemon games
You should rebattle the Elite Four over and over. You should rebattle the Elite Four over and over swapping out every Pokemon in your party.