Kartana

Kartana is a threatening Pokemon in Mix and Mega because it makes good use of its already high Attack, decent Speed, and unique movepool to utilize Tough Claws from Metagrossite. After Mega Evolving, Metagrossite Kartana's base 191 Attack and 149 Speed allow it to outspeed and 2HKO most of the Mix and Mega metagame, including threats like Weavile, Landorus-T, unboosted Zygarde, and Lucarionite Terrakion. Kartana's useful Grass / Steel typing leaves it with a notable resistance to Fairy-type moves like Altarianite Zygarde's Extreme Speed, as well as leaving it with a key resistance to Water-type moves, allowing it to win against Golisopod one-on-one if needed. When Kartana's typing is combined with its base 151 Defense stat after Mega Evolving, Kartana is able to survive powerful resisted attacks more easily as well. However, Kartana's Grass / Steel typing also leaves it with a huge weakness to the common Fire type, which means that it is easily forced out by Primal Groudon as well as Entei and Victini if it isn't running Return. On top of that, by virtue of being a physical attacker, Kartana is easily taken on by physical walls like Zapdos, Will-O-Wisp Mew, and Aggronite Buzzwole, and with mediocre Special Defense, Kartana is left extremely susceptible to almost all special moves.