Dusk, along with Dawn, are the Grotesque Guardians which require level 75 Slayer to kill. It is the boss version of the gargoyle, found on the Slayer Tower's rooftop. In order to access the roof, players must obtain a brittle key from gargoyles while assigned them for a slayer task. Similar to other slayer bosses such as Cerberus and the Abyssal Sire, the Grotesque Guardians can only be killed while the player is assigned gargoyles as a slayer task.
To initiate the fight, players must ring the Cloister Bell in the north side of the roof. This will trigger a cutscene in which the Guardians will awaken, and the fight will begin. Dusk is immune to magic and ranged attacks; only melee attacks will harm it. In addition, if players stand under Dusk, they will be trampled and receive 30-40 damage.
In the beginning of the fight, players must attack Dawn with ranging attacks (as she cannot be harmed with melee and is resistant to magic), as Dusk cannot be harmed during this phase of the fight. Once her health has reached half, both will perform a lightning special attack that has an AoE of 3x3, rapidly dealing up to 5-7 damage per tick. After doing so, she will fly away, and players must attack Dusk.
During this phase of the fight, Dusk's wings may glow, and will perform an explosive attack. If players do not run away from him when he does so, the player will be dealt 30+ damage and be knocked back. In addition, debris may fall around the roof, which can deal up to 10 damage and stun players for a brief period of time. Once his health has reached half, Dusk will perform the lightning special attack once more with Dawn.
After defeating Dawn, Dusk will absorb her essence, and initiate the final phase of the fight. Here, he is stronger, can use magic and ranged attacks, and may drag players to a prison of purple flames. Players must escape the prison (by clicking anywhere outside it), or they will be dealt 60+ damage, which heals Dusk.