Rary's telepathic bond

Rary's telepathic bond is a divination spell that forms a telepathic link to let allies communicate. It was presumably developed by Rary.

Effect
When cast, the spell forges a telepathic bond among intelligent, willing creatures, each creature linked to all the others. The creatures can communicate telepathically through the bond, regardless of language. No special power or influence is established as a result of the bond, and once it is formed, it works over any distance (although not from one plane to another).

A wish spell can make a Rary’s telepathic bond permanent, but it can bond only two people per wish.

Material Components
A piece of eggshell from two different species of creature is required to cast the spell.