Aggron

Mega Aggron carves its niche in the OU metagame as a reliable answer to non-Focus Punch Mega Mawile and Icium Z Kyurem-B on stall teams while being a good entry hazard setter on its own. Its pure Steel typing, gigantic Defense stat, and ability Filter also allow it to deal with some other of the metagame's most common and dangerous physical attackers such as Choice-locked Kartana, both Tyranitar formes, and Mega Pinsir. With a high base Attack stat, Mega Aggron is also able to pressure some other threats to stall teams, such as Clefable and Mega Diancie, unlike stall's other Mega Evolution option in Mega Sableye. Furthermore, its superb movepool makes Mega Aggron capable of using various practical moves in the last moveslot, letting it check different threats depending on the needs of the team it is on. Unfortunately, Mega Aggron needs hard support in form of Wish from its teammates to keep healthy due to its lack of reliable recovery, which distinguishes it from Mega Sableye and even Mega Slowbro. Even with a damage-reducing ability, Mega Aggron's Special Defense is not always sufficient, making it struggle against stronger special attackers such as Firium Z Heatran, Focus Blast Magearna, and Fightinium Z Tapu Lele.