Great Olm

Olm is the final boss in The Chambers of Xeric raid. It is one of Xeric's prized possessions and is a large white dragon.

Attacks

 * Standard attack: Magic attack that can hit through protection prayers.
 * Acid: Olm can throw out small puddles of acid, which poison if stood on.
 * Acid Drip: Olm will target one player and drip them with acid. A puddle of acid will appear under the targeted player, dealing the same amount of damage as the other acid attack. The targeted player should move away from the team, continually moving until the acid is removed.
 * Crystals:
 * Falling crystals: At the end of each phase (and Phase 4's final step), Olm will cause crystals to fall from the ceiling. This has a 3x3 radius which deals damage to anyone in it.
 * Explosive crystals: Olm throws out three crystal bombs, which have a 5x5 radius and deals heavy damage to those hit by it upon exploding.
 * Crystal burst: Olm throws crystal seeds on the ground, which burst for heavy damage if a player is standing on top of them.
 * Dragonfire attack: Olm traps its victims in a wall of dragonfire; douse one section and move out quickly, or those in the targeted area will be hit for heavy damage.
 * "Burn with me!" - Olm targets one player who will yell "Burn with me!", which deals 5 damage on them everytime they yell it out. If another player goes next to the burning player, it will spread onto them, and they will say "I will burn with you.", dealing the same amount of damage onto them.
 * Swap - Olm picks two players and a white aura glows around them. Those two players need to be close to/on each other to avoid taking damage; the further they are, the more damage those two will take.
 * Freeze/Prayer disable: Olm sends bolts of electricity going down or up. Getting hit by them "electrocutes" the player, dealing small damage and disabling overhead prayers.

Fight overview
Olm has four phases, with each successive phase granting Olm more power. Once you pass the barrier you cannot go back; the only way out is to either die (you will be placed outside the portal) or kill it.

To progress, disable both arms. They do not have to be disabled for the first three phases. Under no circumstances should you target the head until the end of Phase 4, as it has a healing aura that recovers any damage it takes.

On Phase 4, both arms must be permanently disabled quickly. If one arm is disabled and too much time passes before the other arm is disabled, Olm will regain control of that arm, and it will return with full health. The left arm will start creating a rejuvenation aura from time to time, during which all damage will heal it instead.

Once both arms are disabled, Phase 5 remains. Olm's head will remain, and it will attempt to kill the team in a final stand. It will use all attacks from the previous phases in addition to crystals falling from above and an occasional life siphon. Kill the head, and claim your rewards once it dies.

Trivia

 * Olm made a teaser appearance on the 2016 Christmas event, where it killed a worker named Ulina.