Going to second Cinccino, that thing is a monster but it needs a decent amount of team support, which makes it a really good choice.
Also, I'm going to throw this set into the mix:
Ability: Super Luck
4 HP / 252 Atk / 252 Spe
-Megahorn / Psycho Cut
I used SubSD Absol on my first team that peaked at #15 and it is an absolute monster (no pun intended xD). It can set up on a ton of different mons in this tier since there are a lot of Psychic-types (Specs Eggy locked into Psychic/Psyshock anyone?). Once it has a Sub up, you're forced to attack it if you want to force it out, and then you can just Sucker Punch for a massive amount of damage, or SD if you think the opponent will try to stall out Sucker Punch. The filler move is the issue here, with Megahorn you lose to Weezing and Muk and sometimes Fighting-types, with Psycho Cut you lose out to bulky Psychic-types and Grass-types that want to try and set up and be cute (Mesprit sometimes, bulky Serperior sometimes). So yeah, it has the right balance of badassery and needing team support!