Tyranitar

Tyranitar's Rock / Dark typing and stellar bulk allow it to act as one of the sturdiest Mega Rayquaza checks when holding a Shuca Berry. These attributes also allow it to check Mega Gengar, which it can also trap with Pursuit, as well as Ho-Oh, Ultra Necrozma, Extreme Killer Arceus, and Yveltal. Furthermore, Sand Stream's boost to its Special Defense allows to effectively check special attackers such as Mega Gengar, Calm Mind Ultra Necrozma, and Yveltal. Tyranitar also has solid utility moves: Pursuit guarantees damage on Mega Rayquaza and can remove Mega Gengar, Stealth Rock is a great boon for any team, and Foul Play does solid damage to almost everything Tyranitar is relied on to check. However, Tyranitar's lack of offensive presence allows a lot of Pokemon to easily wall it, including support Arceus formes, Ferrothorn, and Zygarde-C. Tyranitar's typing also leaves it vulnerable to the Ground-, Water-, Steel-, and Fighting-type moves that are carried by Primal Groudon, Arceus-Ground, Primal Kyogre, Necrozma-DM, and Marshadow, which are all very common. It is outsped by every Pokemon it attempts to check, so it is always forced to take damage. This is exacerbated by Tyranitar's lack of reliable recovery, forcing it to run Rest, which leaves it very vulnerable when asleep. Tyranitar can also be lured and eliminated by sets like Draco Meteor Mega Rayquaza and Focus Blast Mega Gengar.