I Am The Black Swordsman
-Bitter Blade
-Shadow Claw/Sneak
-Psycho Cut
-Dragon Claw
Ability: Weak Armor
Item: Assault Vest
EV's and Nature: 4HP / 252 Atk / 252 Spd
Jolly/Adamant Nature
Primarily for Singles. Bitter Blade is your primary STAB, strong and provides healing. Shadow Claw is secondary STAB, useful for all the Ghosts popping up in competitive lately, while Shadow Sneak is for priority. Psycho Cut is primarily to deal with Clodsire, who eats up Ceruledge otherwise, and also lets you hurt Fighting types easier. Dragon Claw is for catching Garchomp, not-Tera Hydreigon, Roaring Moon, Walking Wake, and whatever other Dragon-types are doing good in the Meta on the switch (whether or not Ceruledge should stay in after the ambush is debatable): it's also a safe prediction move for when you don't know what your opponent will switch in, or you have nothing better to hurt the opponent. (Remember, Dragon is only resisted by Steel and Fairy... One of those is weak against Ceruledge, the other is one you resist.)
Item is to buff your impressive SpeDef stat, and force your opponent to target your Def to take you down, while Ability is to increase your Speed stat; a cruel irony, forcing your opponent to raise your stats for you, but Ceruledge can pull it off.
Jolly is preferred for a guaranteed Speed advantage, but if things work right then you'll be boosting your Speed high enough that Adamant is worthwhile.
Other Options:
-Brick Break = stops Double Screens and counters Normal and Dark types who'd otherwise think they're safe.
-Poison Jab = pretty much exclusive for Grimmsnarl, who otherwise walks all over Ceruledge if it has any offensive attacks besides Spirit Break.
-Iron Head = your best option against Fairies if you must have Super-Effective damage.
-Close Combat = hahaha-no. Don't. Despite the power difference compared to Brick Break, the drop to your Def and SpeDef destroys Ceruledge's best selling point, that it is a tanky sweeper with decent Speed. If you want a fast Ghost-killer that can't take a hit, use Zoroark (either one) or wait for Liepard to be reintroduced instead.
-Solar Blade = if you can ensure the Sun is up, your best option against Water types.
PARTNERS:
-Gardevoir/Gallade
Although stacking a Ghost weakness, there are some advantages to running one of the two on the same team as Ceruledge. Yes, besides SAO jokes about Kirito-Ceruledge and Asuna-Gardevoir.
~Ceruledge nicely soft checks the Fairy types (not named Dachsbun) that would otherwise threaten Gallade, and hard-checks the Steel types that would see Gardevoir as easy setup. Of special note is Corviknight, whom troubles both Gardevoir and Gallade, but can't do much to Ceruledge.
~With access to Thunderbolt (Gardevoir) and Leaf Blade (Gallade), the Psychic Twins can provide cover for Ceruledge's weakness to Water, while Aqua Cutter and Energy Ball also lets Gallade and Gardevoir (respectively) handle most Ground types.
~Despite stacking a Ghost weakness, Gardevoir and Gallade are not helpless against Ghost types. Gardevoir can carry Shadow Ball, which lets her handle any Ghost not named Hisuian!Zoroark, while Gallade can carry Night Slash, which trades a hit on Mimikyu for a sure hit on Hisuian!Zoroark. Any Ghost-type that survives & takes down one of Ceruledge or Gardevoir/Gallade should not be in a position to survive the counterattack, especially a Ceruledge/Gallade combo; both can run Shadow Sneak.
~Gardevoir and Gallade also nicely handle Ceruledge's weakness to Dark types. Gallade's Sacred Sword handles most Dark types well enough, while Gardevoir's Moonblast and Aura Sphere hits almost every Dark type of note.
~If using in Doubles, Gardevoir is a really good partner for Ceruledge, and not just for the not-insignificant offensive pressure mentioned above. Access to Life Dew lets her heal up Ceruledge more than Bitter Blade alone, Icy Wind and Thunder Wave for Speed control, dual-Screens, Will-o-Wisp, Gardevoir can apply offensive pressure to complement Ceruledge and support to make him stronger.
~Gardevoir also counters most Dragon types, who otherwise give Ceruledge trouble, allowing you to swap out Dragon Claw for something else.
-Kingambit
Despite stacking a Ground weakness, this is another Pokemon that complements Ceruledge nicely. That X4 weakness to Fighting becomes a free switch-in for Ceruledge, while Ceruledge's weakness to fellow Ghost types becomes a free switch-in for Kingambit. Furthermore, Dachsbun becomes manageable, as the defensive doggo now has to face a STAB-Steel instead of Ceruledge's not-STABed Iron Head.
-Lucario
Rather hard to not stack a Ground weakness, but consider Lucario a compromise between Gallade and Kingambit. A wide offensive movepool with good anti-Ghost type coverage, and Steel's praised-to-death defensive typing (that Ceruledge's Ghost-typing helps protect)... The main thing Lucario brings to the team that neither Gallade or Kingambit provide is lots of reliable Priority moves. Extremespeed, Vacuum Wave, Bullet Punch... If Ceruledge didn't knock it out, Lucario will finish it.
-Water
Speaking of Ground weaknesses...
~Gyarados is flat-out immune to Ground, using Ceruledge as bait for a free switch-in on any Ground type not named WaterAbsorb!Clodsire.
~Vaporeon can run Wish to keep Ceruledge healthy, Chilling Water to pseudo-buff Ceruledge's lower Defense, Ice Beam to handle Dragons, and Water Absorb so that Ceruledge can bait in Water types. Meanwhile, Ceruledge checks the Grass types that would otherwise take a chance with Vaporeon.