Umbreon is a Dark-type Pokémon from the Johto region. It evolves from Eevee when fed 25 candies after walking an Eevee Buddy 10 km or more, and evolving it still being Buddy during the nighttime in game.
Umbreon - Moonlight Pokémon
Umbreon evolved as a result of exposure to the moon's waves. It hides silently in darkness and waits for its foes to make a move. The rings on its body glow when it leaps to attack.
There is a continuation of an easter egg that refers to the names of the Eevee Brothers, despite the fact that Tamao wasn't member of Eevee Brother, naming Eevee with her name will result in a Umbreon when it is evolved.
Works only once per account and even if Eevee was already evolved into Umbreon not using this method.