As you enter the Champion's Room, you come face to face with a mind controled Ash Ketchum. Mewthree, using Ash as a channel, curses you for coming this far and challenges you to a one-on-one battle.However, after beating him, the mind control does not break. Then Joey comes into the room with Ash's Pikachu on his head. Mewthree gets enraged and appears before you and claims that he will take everybody with him in some sort of suicidal attack. Just in time Mew appears and tell him that, since he is made from Mew's cells, Mewthree is his son. Mewthree finally finds peace and swears to repay for all the damage he caused. Then Ash and Joey start a musical act of Pokérap, with all the sprites of the 150 Pokémon appearing in the scene (Mew was not included in the Pokérap).
For the Snorlax and Primape use any Ghost type pokemon with (recommended) fighting type and psychic moves. Or just use any move using more time. The rest is easy with a level 90+ aqua ringer using ice beam and muddy water or hydro pump. If possible, bring all 3 starters at their 3rd evolution (e.g. Venusaur, Blastoise and Charizard) so you could easily defeat the 3 starters of Ash. Use a Level 83 or higher Gengar with Thunder and Psychic. First, Thunder until Primeape comes out. Then use Psychic until Primeape is gone. Thunder Pidgeot. Then Thunder Squrtile then use Psychic when Bulbasaur comes out. Finally, Thunder Charizard until dead. Don't forget to heal after Pidgeot. Rain Dance is optional. Good Luck!
- Have a lvl.100 grass type that knows solarbeam and leechlife.
Catch/Trade an eevee, evolve it to Vaporeon. Train it to lvl 95-100. Let it learn aqua ring and some strong moves. Set up aqua ring and kill everyone in Ash's team (using different moves for different opponents)
If you don't want to train a lvl 20 pokemon up to level 100, or you don't want to spend time catching an eevee, use a seaking instead. Set it up with aqua ring, teach it a couple of strong attacking moves and kill ash's team