While I myself have not tested all of these movesets, I have a friend who gave it a shot and sent me the link to view them. Anyway, here it is:
Reuniclus Moveset
You are going to want this on your Reuniclus no matter what its role on your team is:
Ability: Magic Guard
Moves:
Psychic: It's a no-brainer, I suggest upping its PP, though.
Focus Blast/Shadow Ball: Focus Blast gives Dark and Steel coverage, but means you have no moves effective against Psychic. Shadow Ball gives Steel and Psychic coverage, but no Dark coverage, meaning you'll have to switch out on a Dark type enemy.
Now this is where the set really changes based on how you're planning on using Reuniclus.
Trick Room Set:
Nature: Quiet
Item: Lagging Tail/Iron Ball/Full Incense
EVs: 252 SpA, 44 SpD, 216 Def
Trick Room: It's literally the point of your moveset and why you even have Reuniclus on your team.
Calm Mind/Shadow Ball/Focus Blast/Recover: Boost your sweeping ability, get coverage of more types, or increase your lifespan, your choice.
Support Set
Nature: Bold
Item: Light Clay/Mind Herb
EVs: 252 HP, 128 Def, 128 SpD
Light Screen/Reflect: Which defense stat is worse on your team overall? Choose the move that covers that.
Recover/Toxic/Thunderwave: Are you trying to stay alive or annoy the enemy? Thunderwave works best in Doubles/Triples, but can be used in Singles.
Sweeper Set
Nature: Modest
Item: Life Orb/Wide Glasses
EVs: 252 SpA, 128 Def, 124 SpD, 4 HP
Calm Mind: Because what's scarier than a maxed out base 125 Special Attack stat? Adding 1/2 of that to the stat for every Calm Mind. Also gives the added bonus of increased resistance to special moves, like Shadow Ball and Dark Pulse which would otherwise threaten Reuniclus.
Pain Split: While it isn't as reliable recovery as Recover, it does do damage to the enemy and can help whittle down tanks and enemies that resist your attacks.
And, last but not least, YOLO Set
Nature: Modest/Timid
Item: Choice Specs/Choice Scarf
EVs: 252 SpA, 252 Spe, 4 Def
Thunder: High Damage, decent coverage, why not?
Energy Ball/Flash Cannon/Focus Blast/Shadow Ball/Hyper Beam: They cover a decent amount of types, and all will definitely hurt the enemy when they hit. Hyper Beam almost guarentees that you'll have to switchout after using it, but with an overall SpA stat of almost 300 with the correct nature and the Specs, a Hyper Beam will annihilate anything that doesn't resist it. It is the Hail-Mary, and as such, do not use it until all other options have been explored.
I hope a least one of these sets are continuously viable, and I hope they were easy to understand. Thanks for reading.