Introduced by the Harken Scythe mod, "Spectral Mob" is a term encompassing all of the mobs able to be summoned by a Harbinger or resurrected by a player. A spectral mob has the same stats as the mob it was originally, in terms of health and movement speed.
If summoned by a Harbinger, all Spectral mobs will attack the player on sight, even if the normal form of the mob is peaceful. The most dangerous of such attackers is the Spectral Miner, which appears to be a floating ghostly "Herobrine," and attacks the player with a pickaxe. All players in range of a spectral miner will receive the Mining Fatigue and Blindness effects until they escape its proximity.
Spectral mobs can also be resurrected from the souls left behind by mobs slain by a weapon enchanted with Soulsteal (as opposed to Soul Stealer, added by the "Soul Shards" mod.) Once resurrected, a spectral mob can be tamed by right-clicking it with a Creepball. The tamed mob will be sitting, and can be commanded to stand and follow the player by right-clicking it with an empty hand. Said mob will then defend the player from all potential threats, much like a tamed Wolf.
Spectral mobs have the same base texture as their normal counterparts, but use a tranparent blue-white color scheme in place of the normal pallete. The only two exceptions are the Spectral Miner and Spectral Villager, which appear as a transparent version of "Herobrine" and a Green villager, respectively.
All spectral mobs use the same sounds as their normal counterparts. The sole exception is the Spectral Miner, which emits an eerie, ephemeral sound when players are nearby, and uses the "damage.hit" sound when injured or killed.
When hostile, spectral mobs will attack their target in the same way as their normal counterpart, or by charging at them if said counterpart is normally peaceful. Spectral mobs are normally spawned without equipment, but humanoid mobs (Skeleton, Zombie, Wither Skeleton, Pig Zombie, Spectral Miner) can be equipped with a tool. If equipped with a ranged weapon, the mob will use it appropriately.
Some issues arise with tamed Ghasts in that their normal free-floating behavior often leads them to fly away from the player that has resurrected them, making them an unfavorable mob to attempt to tame.
All spectral mobs will gradually lose health, losing one health approximately every five seconds. The health of a Spectral mob can be restored either by offering blood from an essence keeper or vessel, or by using a healing staff on the desired mob.