In the rates list, pick Necromancer in the Celestial pool (Click a Class you want the most).
Spin until it lands; the screen tracks progress to a guaranteed Celestial.
Equip Necromancer from the Classes panel.
Dungeon Lootr Class Summon screen with Lucky Spin and Normal Spin buttons, the rarity rates column and the Celestial and Exotic pity counters. Source: YK7kR0aioes at 2:06Dungeon Lootr Celestial summon pool listing Artemis, Vacio, Azure Devil, Necromancer, Forge Archon and Moon Witch. Source: YK7kR0aioes at 2:07Dungeon Lootr Classes panel for Necromancer showing Celestial rarity, Magic archetype and the Grave Retinue mastery passive. Source: -AJtdfvbgmo at 2:42
Overview
Dungeon Lootr Necromancer is a Celestial Magic class from Update 2. The Class Summon screen lists it in the Celestial pool alongside Moon Witch, Azure Devil, Artemis, Vacio and Forge Archon. Its mastery passive is Grave Retinue.