Aggron

Aggron's Mega Evolution boasts a ridiculously high base 230 Defense stat. Furthermore, its ability, Filter, reduces the amount of damage taken from super effective attacks by 25%. Mega Aggron's pure Steel typing gives it ten resistances and one immunity. It has access to great support moves, including Stealth Rock, Roar, Toxic, and Thunder Wave. Mega Aggron has a good base 140 Attack stat, which lets it fire off strong attacks; however, this is fairly average considering that Mega Aggron cannot use a boosting item. Before Mega Evolving, Aggron has a horrible defensive typing, and after Mega Evolving, it misses out on the passive recovery that Leftovers would give it. Mega Aggron also has a fairly average base 80 Special Defense stat and a pitiful base 50 Speed stat.