Having Exclusive Spells defeats the flavor and plot of the mirror mage. You have no skill in magic how the fuck did you uncover a spell.

Reflection prison - you may imprison acperson inside a mirror. They are in a mirror pocket dimension which is like a liminal space → worldbuilding potential. That person sees you instead of themselves in their reflection. Sound doesnt pass through the mirror however you may communicate by breathing on the glass and writting on it, or by other visual or telepathic means.

Each person can have only 1 trapped reflection at a time. If any mirror is broken with your reflection visible the trapped person may exit the mirror as the spell is broken. If the mirror is too small the trapped person is just released from it

Mirror spell - this spell’s names and properties changes to the last spell cast around you