I can elaborate more on these if necessary but here's some things I thought could get a mention to help us get started. Organize how you want as well, idk the exact names of all of them specifically sometimes and still trying to grasp the basics of this thread.
Edit: Had to elaborate so only going to do some for now.
Will-O-Wisp + Roost - S: Set allows itself to be an offensive and defensive presence not only for itself but its teammates as well. Longevity with Roost and cripples physical attackers and switch ins with Will-O-Wisp or strong attacks. Easily implemented on any archetype.
Dragon Dance + 3 attacks - A: Dragon dance sweeper with lack of longevity due to recoil. The metagame trends is what I think makes it fine for an A rank set as it's still an extremely hard hitter regardless.
Roost + 3 Attacks - A: Strong hitter, reliably recovery, but lacks the added power and speed of Dragon Dance. Has a harder time against offense and is generally suited to more balanced/bulky offense teams.
Dragon Dance + Roost - A+: DD sweeper with more longevity thanks to Roost. This is usually the go to set on Zard X in terms of sweeping. Has issues with sand and a handful of scarfers but overall a very reliable set.
Unaware CM and MG CM - A+: MG CM can sweep teams late game after some boosts while Unaware CM breaks stall and defensive set up sweepers like Crocune and MG Clefable more efficiently. Unaware allows it to check general set up sweepers such as BD Azu and NP Thundurus as well.
Cleric - A-: Useful typing and good abilities but for the most part can be a sitting duck and as such has a hard time against more offensive teams or your basic stallbreakers such as Mew and Taunt Heatran. No real offensive presence for the most part.
Thunder Wave - A: Allows Clefable to be a support role for balanced teams to slow down cleaners such as Hawlucha, Greninja, Weavile, M-Gyarados, and so forth. Can either be a status absorber with MG or a check to set up sweepers with Unaware.
Bulky Defog - A+: Longevity with Roost and an EV spread to survive more hits such as HP Ice from LO Thundurus. Fits easily on offensive and balanced teams.
Scarf Latios - A: Revenge killer and has Trick as an asset to cripple mons such as Chansey or general switch ins on Latios such as specially defensive Jirachi and Doublade. A dependency on Tricking the item is what makes this set less viable than its LO attacker set, but is still a solid choice if the provided tools are necessary for your team.
Sub Flail - A-: When it gets down to minimal HP, Flail will topple buildings. The problem is its over dependency at being at that stage. A strong set but can be a bit challenging to pull off well and needs a bit more support to get it to function.
Specially Defensive: Way down low. Mostly for the fact it doesn't really do anything well when using a specially defensive spread. It loses its biggest selling point in being a physical wall while the tradeoff being taking less damage from special attacks.