In the Q/A of Frost Barrows:
Q:
Can I run this script on the mirror client?
A:
Not at this time. Due to limitations in the current versions of the mirror client, this is not yet possible.
Specifically, it cannot be done at this time because of entity loading speeds. When an entity spawns/changes state, the mirror client will not register it right away.
I would of bought it if it supported it.