Prankster Infernape: I think this one would be pretty good. With Prankster Stealth Rock, Taunt, Will-O-Wisp, Slack Off, and Encore to abuse, Infernape could very easily cause some hell for both offensive and defensive teams alike. What sets Infernape apart from other Prankster abusers is his offensive presence, as 104 / 104 offenses isn't too shabby, and STAB attacks in Close Combat, Flare Blitz, and Overheat to bust down walls that have been crippled by his various status moves can be a true life saver for the team. I really like it.
Multiscale Milotic: At first, I thought this would be a really good Theorymon, since taking half damage is pretty awesome. However, for something that's supposed to take repeated hits, I can't see it working out very well. The thing about Multiscale is that it's supposed to be used on offensive Pokemon that need the extra bulk to take a hit only when absolutely necessary. As a defensive Pokemon, Milotic is expected to be able to repeatedly switch into attacks, but Multiscale will only help somewhat in this case, as after a single hit, it's goodbye Multiscale. This problem is more significant if hazards are on the field, which make Multiscale absolutely useless. Not a fan of this one.
Dark Void Liepard: Why didn't I see how broken this was earlier? Prankster with damn near any Sleep inducing move would be incredibly difficult to play around, and unlike Spore, there aren't any safe switches to absorb it, so this could very easily gain momentum at the start of the match. Even though it has 80 accuracy, Dark Void is just so spammable, as putting anything to sleep can easily provide a safe switch for a teammate, and using U-turn to punish the opponent for hastily switching out their crippled teammate is really a nightmare. Besides, I'm more of a dog person, so that's already a big reason there.
Rock Polish Nidoking: This is one step forward, one step back. Getting Rock Polish makes it hard to revenge kill Nidoking without priority, and can make it fairly easy to sweep team thanks to his excellent coverage. Sadly, he has to give up a coverage move to make this possible. You need Ice Beam for Landorus-T and Gliscor and Flamethrower for Ferrothorn and Mega Scizor, so you'll be blocked by one of those parties when lacking the appropriate coverage move. Nidoking also faces competition from Rock Polish Landorus, which has better stats overall, as well as having Knock Off to go mixed. I guess I'm neutral on this one.