Arraghun's spell of Impale

A shadowy creature appears behind a creature of your choice, that creature rolls a wisdom saving throw or be due surprised by this creature. You now have control over this creature. It may attack with the dagger twice a round with a 1d6, has 30ft of movement, 10 ac, 20 hit points with a 10 for all of it's modifiers. When the dagger is not being held by the creature, the spell ends, if the creature is dropped to 0 hit points, the spell ends, if the creature is out of sight from the spell caster, the spell ends, if the creature is 60ft or more on the end of the spell casters turn, the spell ends. When the spells ends, the dagger is dropped if it was a spell casting material, if the dagger was not a spell casting material, it dissinagrates. The fabric is used up.