Charizard with Fire Blast, Focus Blast, Air Slash and Solar Beam with a Charizardite Y.
Rotom-W with Hydro Pump, Thunderbolt, Will-o-wisp and Volt Switch with Leftovers.
Espeon (Magic Bounce) with Psyshock, Calm Mind, Dazzling Gleam and Shadow Ball with Life Orb.
Garchomp with Swords Dance, Earthquake, Stone Edge (for Talonflame and Zapdos) and Dragon Claw with Garchompite.
Mawile (for against Fairy Types) with Taunt (stop status moves and for Sucker Punch), Sucker Punch, Play Rough and Iron Head (for Fairy Types) with Mawilite.
Shuckle: Relaxed nature, Contrary ability. Shell Smash (Contrary increases defenses), Toxic (kinda obivious), Power Split (lower attacks for survival) and Rest. Item Rocky Helmet for lowering HP of enemy with toxic.
Klefki: Bold Nature, Prankster ability. Thunder-wave (slow opponents), Swagger (for Foul Play increase), Substitute (to avoid status moves, encore or taunt) and Foul Play (Swagger increases damage).
Klefki looks much better imo and Twave makes sure Charizard isn't totally useless when not mega. Espeon would benefit too.
Also choose a mega and stick to it. Charizard and Mawile are lame if not mega'd and you are sacrificing their item slots for no reason. --- I am Kruploy; reborn. And I come to you now at the turn of the tide.