Mine is this motherfucker that I used on X to get a 100 battles win streak.

Conkeldurr (M) @ Assault Vest
Ability: Guts
Level: 50
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Drain Punch
- Mach Punch
- Ice Punch
- Knock Off

I always thought bulkier pokemon do better in such a place, that thing confirmed me. Other than Atk, I invested it in Hp rather than SpD, to make it overall bulky, with a raw bulk of 211 / 115 / 129.
It's basically because mostly of the pokemon there doesn't have the power to outdamage it or the bulk to outank it while dealing more damage, and with Drain Punch it has a great sustainability.
Other moves include IPunch for coverage as well as KOff that is also good in longer 1v1 where you deprive enemies of their item, and lastly Mach Punch that besides being a great prio on it, it's capable to one-hit frailer weat-to-it pokemon by itself. Great Partner to it is Aegislash, which is also another extremely good mon.
1v1 almost any mon but fairies and hard-hitting flying types.
As a Pivot It is awesome and 2bh I recommend it to you, even in SM.