Active Soul is a soul item that grants the user an active ability with cooldown. This ability can be used by clicking on the item or pressing the corresponding number for the item slot on the keyboard. Each player can carry up to two active souls. While passive souls can occupy an active soul's spot, the active souls cannot inhabit a passive slot. There are currently not enough active souls to fill all active slots of a full group, so having one active and three passive, or even four passive, is nothing unusual.
Each active soul is better suited to one or two classes but there are no restriction on the items like the Impossible Bosses WC3.
Active Souls List (notation of x / xx / xxx refers to having rank1 / rank2 / rank3 of the soul):
Summon a shadow that has a high priority to be targeted by boss ability casts and attacks. When the shadow dies, it will deal 150 damage to enemies in a large area. Lasts 6.5 seconds and has a 60/50/40s cooldown.