So, we have 4 nominations; Mew, Mega Gyarados, Mega Charizard X and Gastrodon.
Mew -> This thing trolls Team 2 so hard it's not even funny. It comes in on Infernape, Zapdos and Infernape and can pretty much do whatever it wants (Defog, Softboiled, etc) since their attacks don't even come close to KO-ing it. Using Toxic on it is also counterproductive as this leaves Team 2's Zapdos (aka their only answer to Talonflame) on a timer.
Mega Gyarados-> For a supposed "easy win button", having to click Stone Edge most of the time really sucks. Using this also means Team 1 is starting the game fully banking on Gyara to pull off a sweep since without a hazard remover, Team 1 cannot utilize Talonflame and Kyurem-B. It also needs Stealth Rock to be on the field to sweep Zapdos and Infernape.
Mega Charizard X-> This thing is pretty good as it can sweep and provide support for its team but I think it might struggle to do both. Lack of Roost means you are easily worn down, especially when you are 4x weak to Stealth Rock before Mega Evolving. This also hinders its ability to sweep especially when you consider Team 2 has 2 powerful priority users.
Gastrodon -> Not sure about this one since I rarely use Gastrodon. While it looks good, but unless Scald burns Mega Scizor, Mega Scizor can set up and kill it when its HP gets down to about half (+2 28+ Atk Mega Scizor Knock Off (97.5 BP) vs. 252 HP / 200+ Def Gastrodon: 215-253 (50.4 - 59.3%) -- guaranteed 2HKO). This task is not too difficult considering Close Combat from Infernape and EQ from Lando do more than half. Gastro may also find itself worn down over the match when it fails to find a chance to Recover.
Mew -> This thing trolls Team 2 so hard it's not even funny. It comes in on Infernape, Zapdos and Infernape and can pretty much do whatever it wants (Defog, Softboiled, etc) since their attacks don't even come close to KO-ing it. Using Toxic on it is also counterproductive as this leaves Team 2's Zapdos (aka their only answer to Talonflame) on a timer.
Mega Gyarados-> For a supposed "easy win button", having to click Stone Edge most of the time really sucks. Using this also means Team 1 is starting the game fully banking on Gyara to pull off a sweep since without a hazard remover, Team 1 cannot utilize Talonflame and Kyurem-B. It also needs Stealth Rock to be on the field to sweep Zapdos and Infernape.
Mega Charizard X-> This thing is pretty good as it can sweep and provide support for its team but I think it might struggle to do both. Lack of Roost means you are easily worn down, especially when you are 4x weak to Stealth Rock before Mega Evolving. This also hinders its ability to sweep especially when you consider Team 2 has 2 powerful priority users.
Gastrodon -> Not sure about this one since I rarely use Gastrodon. While it looks good, but unless Scald burns Mega Scizor, Mega Scizor can set up and kill it when its HP gets down to about half (+2 28+ Atk Mega Scizor Knock Off (97.5 BP) vs. 252 HP / 200+ Def Gastrodon: 215-253 (50.4 - 59.3%) -- guaranteed 2HKO). This task is not too difficult considering Close Combat from Infernape and EQ from Lando do more than half. Gastro may also find itself worn down over the match when it fails to find a chance to Recover.
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