From Destinypedia, the Destiny wiki
Champions come in three varieties; Barrier, Overload, and Unstoppable. A given enemy race has a Champion for two of the three types, and can be easily identified by red, tendril-like growths and dark coloration.
Each type of Champion has a corresponding type of player weapon or ability that can be used to counter their special attribute. They will stun the Champion temporarily and will notify all nearby players with a sound and a text prompt. Anti-Champion capability can be most easily acquired through the current Seasonal Artifact with unlockable weapon mods and class ability mods equipped on armor. Some Exotic weapons also have Anti-Champion capability.
List of Champions
List of Appearances