Special Sweepers

Mega Altaria

Mega Altaria can become a evry effective special sweeper because of its helpful ability Pixilate and its vast moveset. It also has reliable defenses to allow a setup for the sweeping. The only setback for Mega Altaria is its Speed, but it can be boosted by Agility. IVs should only excluse Attack, and a Modest or Timid nature is best. EVs should be invest in Special Attack and Speed.

This moveset is best for sweeping because of the STAB (Same-Type Attack Boost) and the coverage. With Pixilate, Mega Altaria's Hyper Voice becomes Fairy Type and gains a 30% Boost, like Salamence's Aerilate. Dragon Pulse is obviously for STAB. Flamethrower and Heat Wave is for coverage, namely Steel types, and Flamethrower should be chosen only for Singles and for reliable accuracy. Agility is better for a sweeper to raise Speed, but Roost is another option to regain health.

Move 1: Hyper Voice	Move 2: Dragon Pulse
Move 3: Flamethrower/Heat Wave	Move 4: Roost/Agility

Serperior

Serperior is one of the most powerful special sweeper because of its ability, Contrary, which reverses all stat changes, including self-inflicted. Due to this, Leaf Storm is its main move that deals massive damage while raising Special Attack by two rather than down two. Because of the giant Special boost, Serperior should be Timid to increase Speed. Coice Specs is an options to add more power, but Life Orbs can be used as well to be able to regain health with Giga Drain or Synthesis.

As mentioned before, the main move is Leaf Storm, which buffs the other three moves (if Giga Drain is chosen). Unfortunately, Serperior has a very shallow movepool, so it has to rely on Hidden Power for coverage. The type of Hidden Power varies based on its IVs.

Move 1: Leaf Storm	Move 2: Dragon Pulse
Move 3: Giga Drain/Synthesis	Move 4: Hidden Power (Fire/Ground)

Volcarona

Volcarona is another powerful special sweeper because of its buffing move, Quiver Dance, which raises Special Attack, Special Defense, and Speed. The best item to be held is Life Orbs as well, but Choice Scarf is another option because of its lower Speed, and Fiery Dance can be spammed because of the Special Attack raise. EVs should be invest just the same in Special Attack and Speed, Modest or Timid, but the remaining EVs should be invested in Defense since Sp Defense can be raised by Quiver Dance.

As mentioned before, Quiver Dance is the main move that buffs Volcarona up. Not only is Fiery Dance and Bug Buzz for STAB, but Fiery Dance has a high chance of raising Sp. Attack up one stage, which is why Choice Scarf is useful. The last move can vary; Giga Drain the same reason as Serperior, and Hurricane for coverage and power, although its accuracy is spotty.

Move 1: Fiery Dance	Move 2: Bug Buzz
Move 3: Giga Drain/Hurricane	Move 4: Quiver Dance