Hm, I have no idea how to do this automatically, as I expect you want the reflection to "update" when your character is moving.
You could export your scene as video (without mirror visible), mirror (flip horizontally) the video,
add to scene and mask with a wall with a mirror on and transparent "hole".
Surely this will not be an accurate "mirror", but gives an idea of...
Toystorylab on Vimeo :
Crassitudes (my "Alter Ego") on Youtube: ![https://forum.reallusion.com/uploads/images/fcc4df30-b3a8-40a5-a427-0735.png](https://forum.reallusion.com/uploads/images/fcc4df30-b3a8-40a5-a427-0735.png)