Make it Extremely happy and level it up at NIGHT time
to make it happy
Feed it tons of items that increase stats
Give it Massages
Soothe Bell
Walk around with it
Prevent it from Fainting
Do not feed it herbs
And slowly Eevee will grow to adore its trainer and evolve during the nighttime
Chat with our AI personalities
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.
To make Eevee evolve into an Umbreon, you have to level it up with high happiness at night.
You will need to have your Eevee to full Happiness, then level it up at least once during the night to evolve it into Umbreon.
Eevee doesn't have a set level to evolve into Umbreon. All you have to do to evolve it is max out its happiness at night. ~KKMG1