What constitutes a core? Can I pick any two (viable) Pokemon?
Avalugg @ Rocky Helmet
Ability: Sturdy
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Avalanche
- Recover
- Earthquake
- Rapid Spin
Mew @ leftovers
Ability: Synchronize
EVs: 80 HP / 244 SpD / 184 Spe
Calm Nature
- Psyshock
- Wil-o-wisp
- Defog
- Softboiled
Avalugg walls Mawile and Kartana, and chips them with rocky helmet. Earthquake hits Mawile in case rocky helmet gets knocked off. Avalanche OHKOs Garchomp, and hits Kartana for a modicum of damage. If at sturdy, Avalugg can take a +2 Continental Crush. It also has a chance to survive it if at ~92% or more. It can also spin away rocks, but be wary of rough skin putting you in range of +2 CC.
Mew can burn Garchomp, eating the matchup with Avalugg (or checking Garchomp itself). It can take hits from Rotom, Magearna, and Torn quite well (even knock off in Torn's case). Mew can also remove Garchomp's rocks with defog. You can also stay in on Mawile to burn it, but the same can't be said for Kartana.