Okay but take an Eevee with a standard physical attacker spread. Let’s assume that it gets to use its Z move, perhaps after switching into a Ghost type with only one attack. It now has the following stats:
Attack: 458 (Hoopa Unbound and Regigigas’s are 460) Defense: 272 Special Attack: 226 Special Defense: 332 (Xerneas’s is 324) Speed: 418 (Mega Mewtwo Y’s is 416)
Let’s recall that Eevee also has access to Adaptability, as well as Return. This means that, following the use of this Z move, Eevee is conceivably able to OHKO common versions of the following Pokemon from full health:
Mega Charizard X and Y Azumarill Dragonite (if it wasn’t for Multiscale) Garchomp Mega Gardevoir and Mega Gallade Mega Heracross Keldeo Latios and Mega Latios Mega Lopuny Mega Mewtwo Y Hydreigon Mega Pinsir Mamoswine Rayquaza
And the list goes on. It can outspeed all of these Pokemon as well.
The following Pokemon cen be reduced to less than 90% of their max HP (i.e., they retain 10% of their HP or less):
Mega Rayquaza Kyurem White Salamence Gyarados and Mega Gyarados Primal Kyogre Mega Kangaskhan Reshiram