Newbie here I need some help

[Kanbara0102]

Hello everyone. First of all, I know this question could sound a little bit dumb but I'm completetly new on rom hacking stuff. I'm just creating my first rom hacks for BW and BW2 it just consist on add the exclusive pokemon from Black to White and viceversa and same for BW2 I already modify the encounter lists, but I just want to know how can I add legendary encounters? For example for Cobalion in Mistralton cave it's just the overworld sprite, you talk to him and the fight start, I want to do something similar for Reshiram (in Pokemon White), Zekrom (in Pokemon Black) Keldeo, Meloetta, Genesect, etc. Just place them, interact and the fight begins, I would love if you can help me with that and if there is a way to activate the events after the player beat Pokemon League, N, Ghetsis.

 

My second question is about how can I add the pokeballs on the floor? As I said I would like to add Genesect so I want to add his drives. Thank you in advance to everyone