Conjure Wraith

You call upon the shadowy wraith. For the duration, the wraith will fight a target given to it by the caster. If the wraith kills that target, the caster can assign a new one if possible. If the wraith does not attack within 1 minute, roll a d4. on a 1 and 2, it will return to the Shadowfell. On a 3 and 4, the wraith will attack the caster. 

At Higher levels. When you cast this spell using a spell slot of 7th or higher, you can either choose to increase the duration by 1 minute or to summon one additional wraith.