Its now time for my own submission into this CCAT: OTR Slowking! (Who saw this coming from the OP?)
Slowking @ Leftovers/ Life Orb (my personal preference is Lefties)
Regenerator
Quiet (+SpA, -Spe)
EVs: 252 HP/ 252 Sp. Atk/ 4 Sp. Def
IVs: 0 Speed
-Trick Room
-Nasty Plot
-Surf
-Psychic/Psyshock
Slowking has made his name in the NU meta as a annoying wall, constantly switching out to regain its health. So what happens when you make a Slowking a very interesting wallbreaker who can sweep late-game? I'm not going to say "durr its god erryone use it now!!11," I'll be honest, it has mixed results. However, when you do have a good match with him, what he does is almost overwhelming. With a -Speed nature and 0 IVs, Slowking reaches a mere 58 Speed, where nothing outspeeds it in TR unless you are a Curse user... With more than 2 under your belt. Before a NP, Slowking has a very respectable 328 Sp. Atk, more than enough to rip holes in major threats. After a NP, its able to break walls like its nothing. Its role does not end after an attacker, however, as it has enough bulk to take the majority of Special hits and can set up TR for the rest of the team.
Sadly, the set is not without its faults. While not exactly Physically frail, it doesn't exactly take hits like a champ from that side. Sucker Punch, a somewhat common move in this tier, destroys him, so support to take out things like Absol is recommended. Jynx also presents a problem because of Dry Skin, but can be taken out through boosts from NP, avoiding Lovely Kiss, or just by the fact that the Jynx might not carry Energy Ball. Another TR abuser is also highly advised, as it does not always survive the 5 turns of TR (although it usually does).
Some calcs to show its power (all taken after one NP):
Surf vs Max/ Max Sassy Mesprit (like anyone uses that, but still): 54.4-64.3%
Surf vs Max/ Max Careful Eelektross: 63.37-74.6%
Surf vs Offensive CM Gardevoir at +1: 60.8-71.6%
Psychic vs Max/ Max Sassy Eviolite Roselia: 66.1-78%
So as you can see, it can 2HKO every defensive threat in the Top 10 except for Slowking.
Offensive teams momentum is destroyed by the loss of their Speed, and the fact that they don't carry much bulk doesn't help.
EDIT: I don't know why I didn't bring this up earlier, but for those of you who are looking back during voting, this Slowking makes an excellent check for Klinklang. +1 Return does an average of ~51%, allowing you to narrowly avoid the 2HKO and set up TR. after this, the opponent will either Gear Shift again or go for another Return (which, as I said, does not normally KO), which allows you to get up a NP, destroy the gears with Surf and enjoy the next 3 turns of TR. Also, if Slowking misses the KO (it is not a gauranteed OHKO if Klinklang is at 100%, and the Klinklang is left at like 4%, another slow poke can come in. Heck, even Swellow can come in and kill with Facade at this point.