I'm got tired of this, I do it again and again and again and never becomes nothing, and I'm not using more than the generated test.gba ROM without any patch, and doing of DJG's said, press start and nothing happens
What I'm doing wrong now?
I'm going to assume that SLAKING has everything regarding Mega Charizard, correct? Make sure ALL of the numbers and data are matching between Charizard and its Mega (except abilities, types, and stats [minus HP]). If you haven't already, go to SLAKING and give it an evolution too (Mega Evolution). However this time, you make sure that there is
no item required (EDIT: And it's evolving to its original form). Also, it would be a safe bet to assume that Mega Pokèmon don't have level-up moves? I didn't give my Mega any learn-up moves. Well, check if you did the above at all. Good?
You probably already have done this. Just make sure that you did those things or it will not work. I had a similar issue in the past, and it turned out that I didn't give my mega his mega item. XD The symbol will not show up in battle unless all the requirements for Mega Evolution are filled.
Do you have the item, the Key Stone, in your bag? If you did absolutely EVERYTHING and you did this all on a vanilla ROM, but still get nothing, I'm stumped since I don't know precisely how you inserted it and if you did anything to the code on accident.
If it freezes when you set the vars and give the item, it's your script.
If it simply does nothing in battle, then it's your implementation in GH3S.
Two words of advice, use G3T as it handles Mega Evolution a lot better than GH3S. Or at least, it does from my experience. And two, use the slots between Celebi and Treeko, its much more manageable.
EDIT: Damnit, the opponent can megaevolve their Pokes, but I'm not T-T
Oh, then the requirements to Mega Evolve your Pokémon hasn't been filled properly. You seem to have done it correctly. However, is Slaking Mega-ing to Charizard and Charizard Mega-Ing to Slaking? If so, that's your problem. Use OPEN Pokémon slots. Extend the roster or use the slots between Celebi and Treeko has the others said.