Spectre

Combat
A Spectre is essentially the same unit it was before dying with a few changes. Their movement changes to flying, their current level becomes their Max Level, and their max Morale is cut in half.

The stats provided in the gallery can be disregarded unless you summon then while playing Creation, since there are no gallery-standard Spectres that spawn in-game. Default Spectres have the potential to make good mages as they have one of the highest Stat Growths for Magic and Mana, but you'll have to manually get them every spell.

Overworld
Variable depending on base unit, but default Spectres have no special use on the Overworld.

Breeding
Variable depending on base unit, but default Spectres have low Fertility and Virility, making them poor breeders.

Moneymaking
More often than not you'll want a Spectre for crafting, since no other unit produces Ectoplasm.

Trivia

 * Spectres currently have two separate, but identical entries in the gallery.