Void Baron Galaxis

Void Baron Galaxis is a Prince of the Void and a powerful Voidlord. During the quest From the Abyss, Ogath the Mad sends players to defeat him and take the Galaxis Soul Shard.

Galaxis spawns along with two weaker voidwalkers. When Galaxis gets low on health, he will absorb one of the voidwalkers, destroying it but healing himself. Killing his minions prior to attacking Galaxis removes his ability to use them to heal himself.