And now for a grave
The short version:
- Get the quest from Ungrol the alchemist in Last Hope.
- The Last Hope Graveyard appears near Last Hope. Kill Celia to unlock the Necromancer class (only if you have already read all four pieces of relevant lore).
In practice, this quest is extremely dangerous, and should not be attempted by low level characters, despite being available as soon as you can make it to the world map in Maj'Eyal (level 1 for most characters). Waiting until level 20 or higher is suggested.
The graveyard has an underground crypt with 12 alcoves, each of which contains a coffin. Opening each coffin may generate a random undead boss. These can be quite a bit more dangerous than Celia herself, depending on what gets generated.
If you skip the coffins and go straight for Celia's ritual room, all of the coffins will spring open and unleash the entire set of random undead bosses all at once. Very few characters will survive this.