So - if an Elven Stormcaller casts Call Winds successfully against a Ringwraith on a Fell Beast, and the resist is failed, the wraith is automatically dismounted, as a result of having been knocked to the ground? I can't find a reason otherwise, and am hoping someone can either back that up, or advise where the rules (or FAQ) state otherwise.

The Fell Beast can make the courage roll to remain on the field as a separated mount, but at least based on my reading, the knock prone should cause the wraith to be separated from the mount.

Yes, the wraith is knocked off. Also, since a Fellbeast is Feral, it automatically runs.

Yep. Fell beast bolts automatically and the wraith takes a tumble same as if it were on a horse.

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