From Destinypedia, the Destiny wiki
Champions are special boss enemies introduced in Shadowkeep. They appear in The Ordeal on Heroic or harder, Legend and Master Lost Sectors, seasonal activities, on the Moon, and in the Garden of Salvation and Deep Stone Crypt Raids.
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 capabilities already attached.
List of Champions
List of Appearances