Dragonite.
Need I say more? I will just because I'll get warned for spam if I don't.
Step 1: Use magnezone to kill Ferrothorn, Forretress, and/or Skarmory
Step 2: Set up Dragon Dance while multiscale or lum berry activates
Step 3: outrage GG?
Step 4: profit!!
Dragonite is one of the hardest threats to take down. Any dragonite-user should have Rapid Spin somewhere on their team, which will make it excessively hard to OHKO it, because Multiscale will almost always be in play. Not even Hidden Power Ice or Ice Beam will be able to KO unless its either Specs or STAB. Lum Berry is annoying too because when you think Rotom W can Will o Wisp it, and you might get out with 1 Pokémon left, your opponent says "lol" and kills you.
And then there's Choice Band.
Starboard Driger said:
Then again, it could just light speed curbstomp you, prisoner style, simple as that. I mean, when it says "IMMA VIOLATE YOU", the manliest thing you can say at that point is "...for how long?"
Multiscale active while Outrage literally 2HKO's the metagame, minus Skarmory, Bronzong, (insert magnezone here) and physically defensive Ferrothorn, who is 3HKO'd. Extreemspeed can be used to pick off and revenge kill things from 40%+, depending on how good the defenses are. And then when you expect one of these two, turns out your Dragonite is actually Mixnite with Fire Blast, that KO's your steel switch-in. (assuming magnezone hasn't already.) Dragonite is versatile, and wicked hard to kill, virtually impossible to OHKO. Oh, and he's got Roost, so he can activate multiscale multiple times. I'd also like to throw in the fact that Dragonite resists both Sun and Rain. He can set up on sun with impunity, and abuse rain with Thunder and Hurricane. I find him to be the biggest thread today.