Gold and Silver introduced Dark-type Pokemon and immediately gave that typing to a new "Eeveelution."
Since Generation II and Gold and Silver, Umbreon has been one of the most popular evolutions of Eevee. It received the brand new Dark-typing, which saw plenty of trainers opt to follow the method to obtain it.
This small Pokemon is surprisingly bulky. Its Special Defense is 130, Defense is 110, and 95 HP. In Gold and Silver, Dark-types are only weak to Fighting and Bug. It also has an immunity to Psychic and resists Ghost and Dark.
Note: This article is subjective and reflects the opinion of the writer.
The best moveset for Umbreon in Pokemon Gold and Silver
Once X and Y were released, it was renamed to Feint Attack. In Pokemon Gold and Silver, it was Faint Attack. This is a Dark-type attack that will give Umbreon a STAB and does not miss.
It bypasses the accuracy check and will always land. It has 60 Power, which isn't great but does fine for Umbreon's main damaging attack.
Umbreon will be able to take a ton of damage before being defeated. That should give it plenty of time to use Toxic and poison opposing Pokemon. This strategy will require some patience but will ensure victory. Toxic will slowly chip away at the HP of whatever Pokemon it is used on.
In Gold and Silver, Moonlight works differently to later Generations of Pokemon games. It is a move that restores Umbreon's HP, allowing it to continue battling while Toxic drains the HP of the opponent.
While there is no weather during the day, it restores by 1/4 total HP. If used during harsh sunlight, it restores by 1/2 total HP. Other weather sees it restore 1/3 total HP. At night, the move restores twice as much HP.
Umbreon can learn Psychic via TM in Pokemon Gold and Silver. This will work as a solid coverage move against one of its biggest weaknesses: Fighting-types. Since this is for the in-game story, this will simply help Umbreon deal damage in a way other than Toxic or Faint Attack.