TzKal-Zuk

TzKal-Zuk is the last monster encountered in The Inferno, and currently the strongest monster (based on combat level) in Old School RuneScape.

According to TzHaar-Ket-Keh, TzKal-Zuk is the apparent leader of the feral TzHaar in the Inferno.

During the fight, a shield will appear to protect the player from TzKal-Zuk's attacks. The shield moves, so players will need to move alongside it to avoid taking damage from TzKal-Zuk. The player must be next to the shield before the boss attack animation begins otherwise they will be hit for very high damage. The Protect from Magic prayer will not reduce the damage of a hit taken from TzKal-Zuk.

After a certain amount of time or upon dealing a certain amount of damage to TzKal-Zuk (unconfirmed), a Jal-Xil and Jal-Zek will spawn. Both of these monsters will not be aggressive towards the player upon spawning, but instead will attack the shield. The shield has approximately 600hp and has very slow regeneration. In order to prevent the shield from being destroyed the player must attack each of the monsters in order to make them target the player. If the fight takes too long, another   Jal-Xil  and  Jal-Zek will spawn. When the boss is under 750hp, JalTok-Jad will spawn, The current tactic of dealing with this final stage is to make JalTok-Jad attack you, but not kill it. Instead, protecting from its attacks whilst remaining behind the shield seems to be the best strategy (whilst also trying to kill TzKal-Zuk). Others may choose to try to kill JalTok-Jad, but this may not be necessary be it that TzKal-Zuk by this point is not far from death. At approximately 250hp 4 Jal-MejJak's (Level 250) will spawn in the lava pool near TzKal-Zuk (two on each side). They will heal him 15-20 health every tick until you hit them, at which time they will turn towards the platform and start channeling a meteor storm in a 3x3 area. You will have to step back away from the shield, while still hiding behind it to avoid TzKal-Zuk's attacks.