So, randomly came upon the name Epona looking at monsters in the Planar Handbook.

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Ur’Epona, also known as Epona’s grandchildren, are horselike creatures that can move from plane to plane. Descended through several generations from Epona (a being variously described as a horse-goddess or even the Primal Horse), they derive their power from her.

Does this goddess (?) get a write-up or mentioned elsewhere?

Does she have any kind of relationship with Equinals, or with Vhara? Or even the Equiceph race?