Acererak first appeared as a hulking undead beast, however, this form was a trick to absorb damage and when it was defeated his true presence appeared as a floating skull.
After an arduous battle he was slain by the heroes and his thrall over the elves was ended.
During the events of Rise of the New God, Acererak constructed new tombs within the Feywild and the Shadowfell to siphon the energy of those planes into a third tomb in the Astral Sea where he planed to use the massive amounts of energy to complete his apotheosis and become a god. Acererak watched as the party Pronefest fought their way through his trap-riddled dungeons and taunted them along the way by leaving cryptic clues. He even was able to capture and decimate the soul of Ki-amar after the Genasi went mad. After Acererak's phylactery and god-golem were destroyed he fled back to his original tomb in the natural world and desperately attempted to complete his transformation into a deity, however he was forever defeated by Pronefest on the 120th degree of Hibar in the year 226 DA.