You wait until night and the lvl it up once
Train your Eevee at night and with happiness. It will eventually evolve into Umbreon.
Eevee doesn't evolve into Umbreon with a stone. Eevee evolves into Umbreon when it is levelled up with high happiness during the night.
Eevee's Dark-type evolution form is named Umbreon. In the primary core games, Eevee evolves into Umbreon when it has full Happiness during the night.
Level it up with maxed out friendship at nightime.
Umbreon is the dark type evolution of Eevee
You receive an umbreon from evolving eevee. You need to befriend eevee and then engage in a battle (at night on the game) and it should evolve into a umbreon.
Make Eevee as happy as you can. For Umbreon, level it up at night. For Espeon, level Eevee up in the day.
you have to raise eevee at night
To make Eevee evolve into an Umbreon, you have to level it up with high happiness at night.
Eevee evolves to Umbreon when it has high happiness, and it levels up while it is dark.
You can get an umbreon by getting an eevee from bill in goldenrod city (in a house) and then you can evolve eevee into umbreon by making it happy and leveling it up at night time.
the best ones are Espeon Umbreon Glaceon Leafyeon and Vaporeon