Cresselia is BL under the defensive characteristic of an Uber, the fact that it gets near the offensive characteristic and can fill in support roles is just icing on the cake.
Defensive Characteristic
A Pokémon is uber if, in common battle conditions, it is able to wall and stall out a significant portion of the metagame.
UU list
Absol
Aggron
Alakazam
Altaria
Ambipom
Arcanine*
Azumarill*
Blastoise
Blaziken
Chansey
Claydol
Clefable*
Cloyster
Cresselia
Donphan
Drapion
Drifblim
Dugtrio
Feraligatr
Froslass
Hariyama
Hitmonlee
Hitmontop
Houndoom
Kabutops
Lanturn
Leafeon*
Ludicolo
Mesprit
Milotic
Mismagius*
Moltres
Nidoking
Nidoqueen
Omastar*
Poliwrath
Porygon-Z
Qwilfish
Raikou
Regirock*
Registeel
Rhyperior
Rotom*
Sceptile
Scyther
Slowbro
Spiritomb*
Steelix
Swellow
Tangrowth
Torterra*
Toxicroak
Umbreon
Uxie
Venusaur
Weezing
walled or beaten pokemon are bolded (sometimes it doesn't matter if you can hit it, as it outspeeds and ohkos you back).
asterisks (*) are pokemon I'm not entirely sure on, as it might be possible for them to run a set that breaks cressy, but i haven't seen it/played the matchup out yet, as they're usually out at different points in the game, or they're clefable and have 30 different options
also, unbolded pokemon all have at least one set that cressy can't stop, some have other sets that lose to cressy that may even be more popular (for instance, DD altaria can break cressy, but defensive variants do much worse, and while steelix running a curse set wins, without the stat boost/speed drop gyro ball does very little).
Bolded pokemon may have annoying options (i.e. encore/toxic/trick) but can't really damage cressy especially one using Psycho Shift
so lets organize the lists
Cressy walls: Alakazam, Ambipom, Blastoise, Blaziken, Chansey, Claydol, Cloyster, Donphan, Drifblim, Dugtrio, Feraligatr, Froslass, Hariyama, Hitmonlee, Hitmontop, Lanturn, Ludicolo, Mesprit, Milotic, Moltres, Nidoqueen, Poliwrath, Qwilfish, Sceptile, Slowbro, Tangrowth, Toxicroak, Uxie, Venusaur, Weezing.
Unsure: Arcanine, Azumarril, Clefable, Leafeon, Mismagius, Omastar, Regirock, Rotom, Spiritomb, Torterra
Doesn't wall: Absol, Aggron, Drapion, Houndoom, Kabutops, Nidoking, Porygon-Z, Raikou, Registeel, Rhyperior, Scyther, Swellow, Steelix. Umbreon
a few notes, curse steelix wins, not the standard sets. Nidoking has to hit it with megahorn on the switch or else he dies to psychic before he does anything.
so anywhere from 56% to 74% of the metagame is walled by Cressy. right now i'm unsure on the asterisks, and would like everyone's opinion on those, but i think it'll pan out somewhere in the middle, meaning that only 14-20 pokemon out of 54 can hurt its defensive sets.
I'm assuming a set of:
Cresselia @ Leftovers
Ability: levitate
EVs: 252 HP / 252 Def / 4 SpD
- Psychic
- Signal Beam / Psycho Shift
- Moonlight
- Calm Mind / Psycho Shift
and yes, we know it won't have all those moves at all times, but they are all possible variables of a stall cressy. technically you could include hp ground and knock out a few more pokes, but that's more of an offensive cress set.
Remember, this isn't matchups, as some of these pokemon that can hit it still lose the majority of the time to most cress sets (cough nidoking cough), these are just pokemon that can hit cress hard enough to not be walled with one of their practical sets (sub/cm/encore/signal beam zam could beat it at + 6 + 6 but doesn't do anything outside of beating cress).