Latios (M) @ Life Orb
Trait: Levitate
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Draco Meteor
- Surf
- Hidden Power [Fire]
- Psyshock
At first you might go 'lol role stacking with rotom-w', but if you look at the coverage both of these pokemons give, they are pretty different, and almost cover all the types, making them have somewhat of a good synergy.
The moveset is for having as much coverage as possible, while dealing high damage.
Against Landorus:
252 SpA Life Orb Latios Surf vs. 0 HP / 0- SpD Landorus: 361-426 (113.16 - 133.54%) -- guaranteed OHKO
Latios outspeeds Landorus and ohkos it with a surf, so i dont think i need to show what Landorus can do to latios.
Against Slowbro:
252 SpA Life Orb Latios Draco Meteor vs. 252 HP / 0 SpD Slowbro: 359-422 (91.11 - 107.1%) -- guaranteed OHKO after Stealth Rock
The chances of OHKOing the slowbro is not 100% without stealth rocks, making it a bit bothersome as slowbro can easily risk the hit and twaving the latios, making it not very efficient anymore. The good thing is, if we have stealth rocks down in the field, it gets ohkoed 100% of them time.
If you are worrying about how much slowbro can do,
4 SpA Slowbro Scald vs. 4 HP / 0 SpD Latios: 40-48 (13.24 - 15.89%) -- possible 7HKO
it is not much at all really.
Against jirachi:
252 SpA Life Orb Latios Hidden Power Fire vs. 252 HP / 0- SpD Jirachi: 221-263 (54.7 - 65.09%) -- guaranteed 2HKO
Well, they chose naive as a nature for jirachi, and i dont think it will work well for it. Latios easily 2HKOs Jirachi with HP fire, and it outspeeds rachi, so no problems about flinching with iron head.
252 SpA Life Orb Latios Draco Meteor vs. 252 HP / 0- SpD Jirachi: 166-196 (41.08 - 48.51%) -- guaranteed 3HKO
Even if Jirachi comes in to take the draco for slowbro, it aint going to end well for rachi as 41~48% is a pretty huge chunk. Latios has to switch out after that, but it left some pretty deep scars on the Jirachi.
80 Atk Jirachi Iron Head vs. 4 HP / 0 Def Latios: 112-133 (37.08 - 44.03%) -- guaranteed 3HKO
jirachi 3hkos latios from full health, and maybe a 2hko if it used its life orb too much, but that would not be a problem, as jirachi would only be getting a maximum of 1 hit on latios, unless it icy winds, which does 28.47 - 33.77%. This would result in 77.8% of its hp maximum, if you are very unlucky to get 2 max rolls on the latios.
In conclusion, I think that Latios should be picked on the bases that it can ohko/2hko quite a number of pokemon, its coverage does not clash with rotom-w too much, and it counters the opponent's team.