The Jagged Dagger can only be used by a Wizard that has joined a unit. Before making a Casting roll, the bearer of the Jagged Dagger may make a sacrifice. One model belonging to the bearer's unit is immediately removed from play as a casualty. The bearer may then modify their Casting roll by adding the Wounds characteristic of the sacrificed model to the result.

Note that this is a modifier to the result of a roll – it does not negate a roll of a natural double 1.