Fanatic

A Fanatic is an infected Goblin that appears in the Vault of Glass.

In Destiny
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 2
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.