This is an elite troop that is only trainable in the Frost Outpostif you have 1 level 10 Training Camp.
Soul Reapers are Blue Energy infused and therefore are immune to Wraith Dragon attacks. In addition, they also steal the souls of attackers killed in battle.
If Soul Reapers are used alone in defense against a Wraith Dragon, you will not lose any Soul Reapers, but it will take your loot. If Soul Reapers are used in combination with other troops against a Wraith Dragon: the other troops will engage in combat against the Wraith, but the Soul Reapers will not be harmed.
Your Soul Reapers do NOT have to die in order to take the souls of the enemy troops. You do not have to kill enemy troops to obtain some souls. It seems that Soul Reapers take 1 soul of the enemies troops per Soul Reaper involved in the battle whether the SRs die or not.
The ability to take Souls is exclusive to defending. You will not be able to recover the Souls of enemy's troops while using the Soul Reapers to attack.
This will be updated later when more information is uncovered.
You must have a Reaper Totem for each one these that you train. When a Soul Reaper dies, you do not get the totem back, but you will be able to revive them in the Spectral Ruins. You can obtain these totems from level 7+ mountainsand Anthropus Camps . They can also be purchased from the Shop with Rubies.