Ghoulsteeds and Living Riders
Living riders must pass a DC 13 Charisma check to avoid being killed by their ghoulsteed.
While ghoulsteeds serve the undead without overmuch
complaint, the same cannot be said for living riders. A living
creature who wishes to ride a ghoulsteed must make a DC
13 Charisma ability check before each long rest. On a failure,
that ghoulsteed attempts to kill and devour its rider while the
rider rests. On a success, the ghoulsteed attempts no attack
that day.
Source and licence
From Creature Codex.
Licence: Open Game Content (OGL 1.0a).