I used this to beat Super Doubles:
Gengar @ Gengarite
252 Spe / 252 SAtk / 4 Def
Garchomp @ Yache Berry
252 Atk / 252 Spe / 4 HP
Tyranitar @ Tyranitarite
I don't remember the full spread, but it wasn't the standard 252 Atk, 252 HP.
Greninja @ Life Orb
252 Satk / 252 Spe / 4 Def
Gengar and Garchomp is the lead. It can cover a wide variety of threats. The big thing to think about if you really need to mega evolve Gengar that turn or not because it will lose Levitate. I never really had any issues other than one Ferrothorn which I had my Pokemon team up on. This team also has multiple Pokemon that can defeat the annoying Cresselia that uses Double Team. The 50th opponent should be quite easy since Tyranitar is supereffective against most of the Pokemon. Garchomp also works wonderfully against the Raikou and Entei. Good luck.
FC: 1778-9489-4489 IGN: King Arceus
Safari: Ferroseed, Klang, Bronzong
VGC 2015 Season: 166 CP