I used this to beat Super Doubles:

Gengar @ Gengarite
Levitate->Shadow Tag
252 Spe / 252 SAtk / 4 Def
-Shadow Ball
-Sludge Bomb
-Dazzling Gleam

Garchomp @ Yache Berry
Sand Veil
252 Atk / 252 Spe / 4 HP
-Dragon Claw
-Rock Slide

Tyranitar @ Tyranitarite
I don't remember the full spread, but it wasn't the standard 252 Atk, 252 HP.
-Rock Slide

Greninja @ Life Orb
252 Satk / 252 Spe / 4 Def
-Ice Beam
-Dark Pulse

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.