Question: how to make eevee evolve into umbreon in heartgold?
Answer: After having a full friendship meter and leveling during the night, Eevee will evolve into Umbreon. You can achieve this by battling with your Eevee on the team (without it fainting), keeping your Eevee on the team, giving it berries and protein, as well as giving it haircuts and taking it to the National Park.