Cerberus is a slayer boss that requires a minimum of 91 Slayer to kill.
It drops the crystals required to create each styles best in slot boot, the abyssal dagger and bludgeon and the smouldering stone.
Throughout the fight Cerberus will generally attack with mage (or melee if you're in melee range), however if you are close to Cerb when he spawns the first attack will be ranged. When Cerb reaches 50%~ and 10%~ he will say "Arooooo" and then shortly after three coloured ghosts will appear at the back of the room.
Each coloured ghost represents an attack style you'll need to pray against, red being melee, blue for mage and green for ranged - these ghosts will each fire one shot from left to right a few ticks apart. The attacks of these ghosts will either drain 30 prayer points if you're on the correct prayer or hit you for 30 damage if offprayer.
Decide for yourself which better suits you. You can either choose to tank two of the hits with your health pool, taking 60 damage and losing 30 prayer or pray for all three hits, wiping out most of your prayer but taking no damage.
Cerb also has a second special attack, he will say "Grrrrrrrrrrr" and spawn three pillars of fire randomly in the room, they will generally not land on you but watch out. If they do, you'll take between 7-10 damage per tick until you move / it stops.
This attack can also happen as the ghosts attack, so keep an eye out!
If there is anything you're still not sure on feel free to drop a question below!
Happy slaying