Malamar @ Chesto Berry
Nature: Adamant / Careful
EV's: HP: 252 / SpDef: 148 / Speed: 62 / Att: 36 / Def:12
Superpower is a great move when combined with Contrary. Not only is it powerful, but it gives you the necessary Attack and Defense boost to really pack a punch AND it compensates for Malamar's lower Defense stat. It also gives you a strong fighting type move to take out other Dark types.
Knock Off, while doing slightly less damage than Night Slash, lets you get rid of pesky held items like Leftovers and you still get the STAB from the Dark typing.
Psycho Cut is also STAB.
And the Rest/Chesto Berry combination is extremely useful with Malamar because it allows you time to build up Malamar's stats with Superpower and not fall prey to poison or paralysis. You also get a free heal without having to wait for your Pokemon to wake up so you can keep boosting your stats until you can one-hit K/O everything.
The reason I spread out the stats a bit more is because I feel like Malamar really needed a bit of a speed boost, but I still wanted that extra kick to the attack and defense in case I came across a situation where I couldn't use Superpower. The 252HP / 148SpDef /and at least 60 Speed are really the most necessary for this set, as Superpower makes up for the attack and defense. But feel free to allocate the remaining 48 points to other stats if you feel it would suit you better, this is just my preference.