Nowhere. In my campaign the beholder had comissioned a bunch of ray reflecting mirrors for itself along with ray-reflecting rotating doors of bronze.diaglo said:[..]
where in the rules does it say mirrors reflect spells? or supernatural abilities?
[..]
The key to winning against him was destroying mirrors and / or use them to counter with their own ray spells. However, due to total lack of light, appropriate darkvision was required.
Regards,
Ruemere
PS. For those who care: Charch-Pachn, one of the lords of Pact of Quaan from Banewarrens.