When these Vex touch a player, they will explode, dealing massive damage. When they are killed, they leave a medium-sized green puddle on the ground. If a Guardian steps into the infected puddle, they are marked for negation. If a Guardian is marked, they must either be cleansed by a relic, or the lit circle in the center of the room. Uncleansed players will be killed when The Templar fires his Ritual of Negation.
In Destiny 2Edit
In Destiny 2, Fanatics can spawn as normal infantry when in Vex-populated planets, such as Nessus. They appear as beheaded Goblins with many sparks around them. When a Guardian gets close to a Fanatic, they explode, dealing massive damage, while also leaving behind a small Vex radiation field that deals continuous damage to Guardians that linger within. When in combat, Fanatics generally march towards Guardians while firing at them with their rifles; however in some cases, they will begin to run and chase after Guardians in an attempt to blow them up.