In order to OHKO Mega-Scizor, Heatran, (After SR Damage) Toxapex, Kyurem-Black, Latios, Defensive LandoT (not star wars lando, Nuivo), Victini, Tapu Koko runs Choice Specs.
You want to defeat Garchomp? Scarf Garchomp can OHKO Tapu Koko easily. And Tapu Koko can OHKO Chomp with HP Ice easily.
Vs Stealth Rock Chomp (Smogon Set) with Life Orb
252 SpA Life Orb Tapu Koko Dazzling Gleam vs. 4 HP / 0 SpD Garchomp: 315-374 (87.9 - 104.4%) -- 31.3% chance to OHKO
Or 68.7% chance to 2HKO
252 SpA Life Orb Tapu Koko Hidden Power Ice vs. 4 HP / 0 SpD Garchomp: 317-374 (88.5 - 104.4%) -- 31.3% chance to OHKO
Or 68.7% chance to 2HKO xD.
And,
252 Atk Garchomp Earthquake vs. 0 HP / 0 Def Tapu Koko: 374-444 (133 - 158%) -- guaranteed OHKO
Vs Stealth Rock Chomp (Smogon Set) with Choice Specs
252 SpA Choice Specs Tapu Koko Dazzling Gleam vs. 4 HP / 0 SpD Garchomp: 362-428 (101. 1- 119.9%) -- guaranteed OHKO
Or 0% chance to 2HKO
252 SpA Choice Specs Tapu Koko Hidden Power Ice vs. 4 HP / 0 SpD Garchomp: 360-428 (100.5- 119.5%) -- guaranteed OHKO
Or 0% chance to OHKO.
Smogon Chomp Sets:
Stealth Rock
Garchomp @ Dragonium Z
Ability: Rough Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Stealth Rock
- Earthquake
- Outrage
- Swords Dance
Swords Dance
Garchomp @ Groundium Z
Ability: Rough Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Fire Fang
- Earthquake
- Outrage
- Swords Dance
Scarf
Garchomp @ Choice Scarf
Ability: Rough Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Stone Edg
- Earthquake
- Outrage
- Fire Fang
Mega
Garchomp-Mega @ Garchompite
Ability: Rough Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Fire Dang/ Stone Edge
- Earthquake
- Outrage
- Swords Dance
These set are running the same EVs and Nature.
Smogon Garchomp Page
Smogon Damage Calc Page (Not plagiarizing, HT)
Choice Specs is better than Life Orb.