At third level your otherworldy patron bestows a gift upon you for yoir loyal service. The following is an option meant to add to those in the Player's Handbook.

Your Patron gives you a small shard of an ancient mirror that reflects a dark version of the world. While the shard is on your person, you know the mirror image spell and can cast it once without using a spell slot. You regain the ability to do so after a long rest. It doesn't count against your number of spells known.

In addition whenever you cast an illusion or conjuration spell you can ignore the verbal components of the spell.

If you lose your shard, you can perform a 1-hour ritual to receive a replacement. This ceremony can be performed during a short or long rest, and it destroys the previous shard. The shard shatters into glass dust when you die.