I am having the same problem and need help urgently! My party consists of:
Gengar big Root
-Hypnosis
-Dream Eater
-Giga Drain
-Shadow Ball
Blaziken @Evioltite
-Bulk Up
-Close Combat
-Flare Blitz
-Shadow Claw
Tyranitar focus Sash
-Earthquake
-Fire Punch
-Stone Edge
-Crunch...