Threats
Keldeo @ Choice Scarf
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Scald
- Hydro Pump
- Secret Sword
- Stone Edge
Keldeo does a good job of keeping both of these Pokemon in check with its typing defensively and its STABs, being capable of outrunning +1 Mega Tyranitar and KOing it with Secret Sword. VS Keldeo it is able to OHKO it after it uses any move other than Hydro Pump, and it doesn't really fear anything from the listed set other than Gunk Shot, which 2HKOs.
Breloom @ Life Orb
Ability: Technician
EVs: 252 Atk / 4 Def / 252 Spe
Adamant Nature
- Spore
- Swords Dance
- Mach Punch
- Bullet Seed
Breloom has access to STAB Techician Mach Punch, guaranteeing the OHKO against it. While it can't OHKO a neutral Greninja with Mach Punch, it deals very heavy damage to it regardless–giving it a good chance to KO after 3 turns of LO recoil.
Partners
Latios @ Life Orb
Ability: Levitate
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Draco Meteor
- Psychic
- Surf
- Roost
Latios provides a buffer versus Keldeo while providing useful wallbreaking power in the process. Keld+Tar teams do kinda give this core a headache though, so Surf is preferable to HP Fire for its ability to 2HKO uninvested Tar which try to switch in on+trap Latios.
Latias @ Soul Dew
Ability: Levitate
EVs: 4 Def / 252 SpA / 252 Spe OR 160 HP / 96 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Draco Meteor
- Psyshock
- Healing Wish
- Roost
Latias provides a much more sturdy buffer versus Keldeo while also having access to Healing Wish, which Tyranitar absolutely adores due to the fact that it allows it to play much more recklessly early-game. The second spread allows Latias to take 2 Icy Winds from Choice Specs Keldeo if Stealth Rock is not on the field. If you're running the max SpA spread, Colbur Berry+HP Fighting is an option over Soul Dew+Draco Meteor to take advantage of people who try to trap Latias with Tyranitar, taking the Pursuit or Crunch (the latter if at full health) and 2HKOing it after Stealth Rock.