A+ Rank
Blastoise (Mega)
no.
Darmanitan
Rock Slide and Flare Blitz KO. 252 SpA Thundurus-T Thunderbolt vs. 0 HP / 4 SpD Darmanitan: 256-303 (72.9 - 86.3%) -- 81.3% chance to OHKO after Stealth Rock
Check.
Florges
Obviously walls but cannot do much back.
Check.
Suicune
no.
Umbreon
252 SpA Thundurus-T Focus Blast vs. 252 HP / 252+ SpD Umbreon: 170-202 (43.1 - 51.2%) -- 53.1% chance to 2HKO after Stealth Rock and Leftovers recovery
Again no Life Orb. So technically not a check, without factoring accuracy.
Victini
Never OHKOs Victini, Victini OHKOs, but is outsped.
A Rank
Celebi
Cannot do anything back. Is never 2HKOd. If you want to say Ancientpower counts go ahead, but this is a
Check.
Chandelure
Scarf checks but otherwise flat out loses under any circumstance.
So... I guess you can say
Check.
Chesnaught
HP Ice 2HKOs, factoring Rocks and Leftovers. SpDef Chesnaught wins but don't use this.
Cloyster
lol.
Crobat
no.
Forretress
2HKOd, etc.
Heracross
Scarf is a shaky check, but regardless:
Check.
Hippowdon
252 SpA Thundurus-T Hidden Power Ice vs. 252 HP / 0 SpD Hippowdon: 186-220 (44.2 - 52.3%) -- 18.4% chance to 2HKO after Stealth Rock and Leftovers recovery
Life Orb 2HKOs. Needs Stone Edge to do anything back, so not calling this a check.
Manectric (Mega)
They both 2HKO each other, but Manectric does not need to rely on Focus Blast. Definitely a
Check.
Metagross
252+ Atk Metagross Zen Headbutt vs. 4 HP / 0 Def Thundurus-T: 198-234 (66 - 78%) -- 25% chance to OHKO after Stealth Rock
252 SpA Thundurus-T Thunderbolt vs. 252 HP / 4 SpD Assault Vest Metagross: 117-138 (32.1 - 37.9%) -- guaranteed 3HKO after Stealth Rock
But Metagross is slower.....
Check.
Nidoking
is 2HKOd, OHKOs, is slower.
Check.
Reuniclus
252 SpA Thundurus-T Thunderbolt vs. 252 HP / 0 SpD Reuniclus: 183-216 (43.1 - 50.9%) -- 3.9% chance to 2HKO
Loses to Life Orb. Can not OHKO. Even with Rocks.
Roserade
Is 2HKOd and cannot OHKO, even with Rocks.
Shaymin
Gets 2HKOd but again cannot OHKO even with Rocks.
Starmie
no.
Zygarde
Never OHKOd unless Life Orb is factored in, KOs, is unfortunately slower
A- Rank
Absol (Mega)
Outspeeds only after mega evolving and they OHKO each other, so not exactly a check.
Aggron (Mega)
Nope. Isn't OHKOd but can't in return without Head Smash which is extremely bad.
Arcanine
Flare Blitz + ESpeed OHKOs. LO Flare Blitz or SR and Flare Blitz KOs. Thunderbolt never KOs even with Rocks.
Check.
Azelf
Obviously a
check.
Doublade
Escavalier
Gastrodon
Jirachi
Krookodile
Kyurem
Machamp
Nidoqueen
Smeargle
Tentacruel
Toxicroak
Trevenant