Ashen Phoenix

Necromancers consider having a phoenix under their power to be a great achievement. This is due to the very brief death cycle of a phoenix. The necromantic ritual must be done with very precise timing after the phoenix dies but before the phoenix is reborn. The phoenix's dying blaze starts in a split second, so the corpse is almost immediately charred.

Despite being difficult to obtain, ashen phoenixes are relatively easy to lose. Anything that would kill an otherwise normal phoenix will complete the phoenix's death-and-rebirth cycle and break the necromancer's spell.