Umbreon's ability to Synchronize means that it makes the status of itself and its foe the same (in battle). For example: If you are fighting an Umbreon and you use Thunder Wave on it to paralyze it, your Pokemon will also be paralyzed. Syncronize works for poison, burns and paralyzation (but not sleep or frozen status conditions). However, outside of battle, Synchronize increases the chance of you meeting Pokemon with the same nature.Evolution
Eevee evolves into Umbreon if it reaches its maximum happiness level at night time. (here for more details)Appearance
Umbreon resembles a canine (exactly which species is uncertain) with a black coat of fur. It has yellow bands around its ears and tail and yellow rings upon each leg and its forehead. They glow when Umbreon is excited and/or attacks, as well as if there is a full moon. Umbreon also has big pretty red eyes.