Superpower SCYTHA
Gives it a powerful Fighting-type coverage move to hit Steel and Rock-types. This means mons like Probopass and Klingklang now fear switching in.... Now, if only it got Bullet Punch, it would be a Bug/Flying Scizor...
Will-O-Wisp Mesprit
Gives it a way to cripple physical attackers that may try to Knock it off and also puts anything else on a timer. Water Veil Floatzel can beat it, though.
Slack Off Garbodor
Makes it a very good wall, now having recovery and that's all it needs to be better. Recovery + Good bulk + Toxic immunity = Rise in viability, maybe even BL3 or RU.
Nasty Plot Pyroar
Makes it kinda like a faster Houndoom, which could improve it greatly. Fire/Normal has pretty decent Neutral coverage, and if Pyroar forces a switch, then it may spell the end for the opponent.
My nomination: Bellosom + Fairy-type + Moonblast, Fairy Wind, and Play Rough
Bellosom is outclassed in 9000 ways by the destroyer of worlds, Vileplume, and to a lesser extent Roselia. Even the oddball Swords Dance set is generally outclassed by Leafeon and Victreebel. But, with a Fairy-typing, Bellosom all of a sudden holds a huge niche as a good defensive Fairy-type or a Physical Fairy that isn't the ultra rare Snubbull. And the only other viable Fairy-types in NU are... Mega Audino...and Clefairy... Marill?... The Poison weakness is a problem, but hey, it wouldn't completely ruin it.