Yeah, to back up what PeterHolmes74 said, Metagross should be running Meteor Mash, EQ, Thunder Punch, and Zen Headbutt generally. I would invest fully in Attack and Speed, as this thing can be pretty fast, unlike the non-mega. I believe 55 out of the 100 points from mega evoing went into speed. 252ATK, 4SpDef, 252 SPE.
D. Snorlax is fine IMO, you could run Bulk Up+Synthesis, but you lose on coverage, though you don’t really need it.
Gardevoir @ Choice Scarf
Ability: Trace(Synchronize works ig, but Trace can be nice, like for reversing London’s TR. Or getting Moody or Speed Boost off of Kayla)
252 SpA, 4 Def, 252 Spe
- Shadow Ball/Focus Blast
Since your Volcarona is Bold Nature, you could run the bulky sweeper set, which allows you to set up more easily. IK it says Timid, that’s pretty much always preferred, but Bold could work with this set.
Volcarona @ Passho/Life Orb/Leftovers(basically whatever you want)
Ability: Flame Body
EVs: 248 HP / 8 Def / 252 Spe
- Quiver Dance
- Safeguard/Giga Drain/Psychic/Bug Buzz
I believe Gyarados for the E4 and E4 only runs:
Gyarados @ Leftovers/Life Orb
252 Atk, 4 Def, 252 Spe
- Dragon Dance
- Custom Move Grass
Since you have FWG and 2 of FSD, I’ll pull a dragon to finish the core.
Garchomp @ Lum Berry/Life Orb
Ability: Rough Skin/Sand Veil(generally Rough Skin is better, but Veil might help with Eduard)
252 Atk, 4 SpDef, 252 Spe
- Swords Dance
- Stone Edge/Fire Fang
- Outrage/Dragon Claw
You could run Band/Scarf, just replace SD with the other coverage move. Naive also works if you are planning to run Fire Blast.