Umbreon (the Moonlight Pokémon) is an exceptionally rare Dark-type Pokémon found among grassy plains and forests within the Unova and Kalos regions as well as the Hoenn and Sinnoh regions on rare occasions. The direct result of Eevee mutating under the enchanting glow of moonlight, Umbreon are cautious hunters that wait silently in darkness before striking out at prey and opponents alike, in turn making them perfect partners for trainers looking to spring a little bit of a surprise on the opposition. Unless you're particularly fond of the moonlight or otherwise think you have the guts needed to take one of these beasts on at their strongest, you would best be wary of these creatures when the moon is out, for as long as they have the light of the moon on their side, there isn't a whole lot out there capable of beating them in a fair fight!
In this evolution, Eevee that possess incredibly strong bonds with their trainers are mutated by the elegant glow of moonlight, transforming them into shadowy beasts that utilize the moon as a direct source of power; a similar effect is generated when in the presence of a Moon Shard, but due to the unbelievable rarity of these items, the use of real moonlight is generally preferred. Both Espeon and Umbreon are considered to be the strangest Eevee evolutions (with the striking exception of Sylveon) because of their unique circumstances; evolution via friendship has always been a relatively mysterious process, but these two creatures take it one step further with their bizarre day/night separation. In the case of Umbreon, a minor alteration in the sun's rays (as moonlight is simply the result of the sun's rays reflecting off the moon's surface) causes a major genetic alteration, reconfiguring their cellular structure in such as a way as to make their power completely dependent upon the time of day. Umbreon are far more hostile and aggressive than Espeon, but they still maintain a high degree of loyalty towards their trainers and other people; as such, they are generally docile in public, though wild ones are considered to be extremely dangerous. Moreover, they are a bit more difficult to train than Espeon as their range of attacks is fairly limited outside of a few weak physical attacks and a Last Resort attack. Even so, the ability to harness unique moves such as Moonlight and Guard Swap can make them troublesome under the right circumstances.
Umbreon prefer to stay hidden from sight during the night, silently lurking around within the darkness as they search for prey. For reasons still not understood, the faint rings patterned on their fur and skin glow faintly in the darkness and only increase in intensity when they are attacking, excited, or are exposed to direct moonlight. This striking appearance tends to have the effect of scaring anyone that suddenly gazes upon them, especially because Umbreon will never move until their onlooker decided to move first. What seems strikingly odd, however, is the bizarre power that Umbreon gain from exposure to direct moonlight; while the effects vary widely, such light generally increases their attack strength, physical durability and movement speed by as much as ten-fold, in turn heightening the threat they pose to astonishing levels. During the day, though, Umbreon are relatively limited in terms of sheer power and instead must rely on their superb defenses alone as protection. If agitated, however, Umbreon can and will release poisonous sweat from glands all over their body to distract an opponent; while the poison itself is nowhere near lethal, it can still serve a useful defensive purpose as it is extremely painful and irritating when exposed to sensitive areas such as the eyes.
Living and walking only by the light of the moon, Umbreon are powerful creatures that can weather many blows before being taken down and can thus be seen as nifty alternatives for defensive tacticians to turn to. With the highest base Special Defense stat out of all Dark-type Pokémon (tied with Hoopa in its Unbound Forme) and a cautious nature only intensified by their inherent loyalty, it can definitely be said that Umbreon are far more durable than they initially appear and can easily prove to be a real nightmare if fought without preparation. If you do choose to battle with one of these strange creatures, though, try to only do so when the moon is at least somewhat bright outside, lest you find yourself backed into a corner with nowhere else to go on the night of a new moon!