The Demogorgon raid is divided in three phases.
First phase: Demons will be spamming from the rifts across the room, so it is recommended to close them. It is usually a good idea to bring all demons to the central area, in order to let all the players focus their attacks on them.
Second phase: The demon Goristro appears, and from time to time he will do a charge attack against any of the participants. It is necessary to draw Goristro onto the yellow runes in the room to weaken him. Note: the black runes in the room will heal Goristro, so keeping him away from those will shorten the battle significantly. One of the simplest strategies is to locate a yellow rune, and stand with it to your back. This way if Goristro makes a charge attack against you, you just have to turn the camera and point toward the rune. After two charge attacks, the Demogorgon is going to attack from above with a ray that can deal a lot of damage, but that can be avoided by standing in the blue areas.
Third stage: Finally it's time to fight the Demogorgon himself. Every player will continuously receive stacks of “madness”, that can only be cleansed in the blue areas. It is a good idea to fight near one of these blue zones so the cleansing process becomes much faster.
Rewards: Demonic Ichor, Protector Seals, minor enchantment materials (such as Peridot) and Salvageable Rings ( including 145 double slotted rings) are CHEST rewards, regardless of what medal your team earns. Demogorgon Fang, a crafting component for Black Ice, is also a possible chest reward. Instance rewards received immediately after defeating Demogorgon are influenced by whether you place Gold, Silver, or Bronze, and the chance of getting a ring is increased by earning Gold.