I've found that for my Malamar some diversity worked very well....
Here's my current set for competitive use.
Malamar @ Muscle Band or Focus Sash
Nature: Adamant
Ability: Contrary
IVs: Speed, HP, Attack
Evs: 252 Spe, 127 Atk, 127 HP
Moveset:
Hypnosis
Topsy-turvey/ Night Slash
Psyco Cut...