Extreme Evoboost increases the user's Attack, Defense, Special Attack, Special Defense, and Speed stats by two stages each. Extreme Evoboost will be unable to increase a stat that is already at +6; if all stats are at +6, Extreme Evoboost can still be executed, but will be unable to increase any stat.
Extreme Evoboost is a Z-Move rather than a Z-Power Effect added on to an existing status move, and therefore interacts with move-modifying effects such as Simple and Contrary normally.
Eevee's Trainer strikes a series of poses to build Z-Power. Eevee then releases a rainbow-colored pulse of energy from its body, summoning one of each of its evolved forms to its position from nearby areas. Each of its evolutions then becomes surrounded in an orb of energy that matches their color and rises into the air. Each of them then fires a beam of energy at Eevee, causing it to become covered in a rainbow-colored aura and get powered up.