Gyarados

Mega Gyarados's access to Crunch in combination with its ferocious Attack stat and acceptable Speed stat makes it a considerably more threatening Dragon Dance sweeper that is capable of taking huge chunks out of opposing teams. Gyarados has phenomenal bulk for an offensive Pokemon and retains critical resistances and immunities in both its Mega and non-Mega formes. Its typing, combined with Intimidate, allows Gyarados to excel not only as an offensive sweeper but also as a supportive defensive wall, checking multiple threats such as Mega Charizard Y and Volcarona. Gyarados also has decent coverage throughout its limited but helpful movepool, although it generally has a hard time fitting all it needs onto a single set. Furthermore, having Mold Breaker in its Mega forme allows Mega Gyarados to break through certain abilities, such as Unaware, Sturdy, Magic Bounce, and Water Absorb. However, both Gyarados's base forme and Mega forme are prone to residual damage, especially Stealth Rock, and its lack of reliable recovery means that this damage will be present throughout the battle. Gyarados's Speed, while not unsalvageable, is also quite mediocre in a metagame full of speedy offensive threats, meaning that even after a Dragon Dance, there will still be certain Pokemon that outspeed Gyarados.