Fine, let's use a Competitive Pokemon, I have a choice between:
Wigglytuff
Milotic
Gothitelle
Meowstic (female)
Ok I probably won't use Gothitelle unless complex bans happen this generation, allowing BL Gothitelle to stay in BL and Competitive to drop down to Wigglytuff's tier. Gothorita could be a possibility in lower tiers if you really want to use a Competitive Pokemon though. Milotic is the best Pokemon out of the bunch; bulky and now powerful, and he doesn't really have a need for the other abilities available to him, though Marvel Scale is nice. We don't really know how Meowstic (female) will play out but I'm willing to bet he will play out better than Wigglytuff.
Arch there are a hell of a lot of Pokemon that can run that.
Celever: /dexsearch Light Screen, Reflect, Stealth Rock, all: Clefairy, Clefable, Jigglypuff, Wigglytuff, Mew, Pineco, Forretress, Magcargo, Swinub, Piloswine, Corsola, Smeargle, Celebi, Lunatone, Solrock, Baltoy, Claydol, Metang, Metagross, Jirachi, Deoxys, Deoxys-Attack, Deoxys-Defense, Deoxys-Speed, Turtwig, Grotle, Torterra, Bronzor, Bronzong, Mamoswine, Uxie, Mesprit, Azelf, Arceus, Arceus-Bug, Arceus-Dark, Arceus-Dragon, Arceus-Electric, Arceus-Fairy, Arceus-Fighting, Arceus-Fire, Arceus-Flying, Arceus-Ghost, Arceus-Grass, Arceus-Ground, Arceus-Ice, Arceus-Poison, Arceus-Psychic, Arceus-Rock, Arceus-Steel, Arceus-Water, Carbink
Ckarasu I feel like people think that RU is the shitmons tier NU the shit shitmons tier. Sceptile is very viable in UU, you have Slowking in RU, Druddigon in RU. Durant was banned from RU for a while but he's in it now. The pokemon in RU are not complete shit - Quagsire was a titan of Adv OU (I think, never really played the tier but I know a bit about it) and he's down in RU. Aggron can take out most of OU with Head Smashes and he's in RU, a hell of a lot of fantastic Pokemon that are being hyped this generation are in RU. Clefable, Galvantula, Absol, Aggron, Aerodactyl, Manectric. I would say that Cryogonal is viable in OU too looking at one I've seen people using - yet to try this though. Wigglytuff was shit in PU, Fairy-Type gives it a "niche" that leaves it flawed by Clefable still, even if Clefable moves up it has few niches, and most are not good ones.