Umbreon first appeared as an Eevee in The Rivalry Revival, where it was used in a battle against Ash and his Pikachu. Brock commented that, by the looks of its shiny coat and bright eyes, that Gary trained it very well. In battle it backed up this observation with a Reflect the likes of which Tracey had never seen before. The Reflect absorbed Pikachu's Quick Attack and although Eevee was sent flying, it landed on its feet having sustained little to no damage. Eevee dodged Pikachu's Thunderbolt attack with Double Team, although its own Take Down was blocked by Pikachu using Agility. It finished the battle by hitting Pikachu with Skull Bash just as Pikachu attempted Thunder. Pikachu's attack shocked itself and, combined with the damage from Skull Bash, knocked it out of the battle having not landed any damage on Eevee.
Umbreon dodging Alakazam's Dynamic Punch
Gary took Eevee with him when he left for the Johto region. It evolved sometime prior to the episode Power Play!, where it was shown to be battling Alex Davis's Alakazam. Gary noted that Alex Davis was the first new opponent it had had in a while. It proved itself to be a very agile battler, dodging Zap Cannon, Headbutt, and Dynamic Punch. When Alakazam used Double Team Umbreon sensed the real Alakazam and slammed it onto the ground. Alakazam used Teleport to avoid Umbreon's Quick Attack, but Gary and Umbreon detected the charging Hyper Beam and dodged it, then knocked Alakazam out with Hidden Power, winning the battle without having taken a single blow. Ash enthusiastically challenged Gary, but Gary declined as Umbreon had defeated Pikachu before, along with that his remaining team did not impress him. Later, Gary and Umbreon helped Ash foil one of Team Rocket's plans as Umbreon severed a cable to their mecha with Tackle. It later illuminated a room with Flash so that Ash could find the lever to the dam mechanism. It then added its own strength to the effort to turn the lever, which ultimately succeeded.
It was not used in Gary's battle with Ash at the Silver Conference, although it did appear on his profile. Gary left Umbreon at Professor Oak's lab when he left on adventures with just his Blastoise.
It appeared again along with its Trainer in Ill-Will Hunting! where it repelled a Golbat from one of J's henchmen with Sand Attack. Gary's knowledge of the area combined with Umbreon's agility resulted in the Golbat accidentally disturbing a hive of Beedrill, which distracted the henchmen long enough for Gary, Ash, Brock and Dawn to escape with the Shieldon that J was hunting. It was called on again to sabotage J's ship, using Shadow Ball to cause explosions and then tackling J's henchmen with Electivire to allow Ash to retrieve Shieldon.
Gary used Umbreon to battle Ash's Gligar in a practice match in Fighting Fear with Fear!. Gligar fled from Umbreon's Shadow Ball, showing that it was unable to battle because of its phobia. Gary called off the battle and gave Ash a Razor Fang to evolve it.
As an Eevee, it was pointed out by Tracey that it was well trained due to its bright eyes and glossy coat. Like its Trainer, it was shown to be confident and smart. Umbreon was also a very adept battler, not being hit by an attack on screen until its last appearance.
A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.
Of all Pokémon used by rivals, Umbreon has used the most moves, a total of 11.
Despite debuting at the end of the Orange Archipelago saga, Umbreon was not shown to be damaged by an attack until the battle with Saturn's Toxicroak, its final appearance to date.
Gary's Eevee and it being used to battle Pikachu during the first battle between Ash and Gary are references to Blue's Eevee and the first rival battle between it and the player's Pikachu in Pokémon Yellow.
For more information on this Pokémon's species, see Eevee and Umbreon.