I'm a new DM running a 5e combat encounter in which the NPC attacker is mounted on a Riding Horse.
One of the players' characters has just cast Confusion, which indicates that
Each creature in a 10-foot-radius sphere centered on a point you choose within range must succeed on a Wisdom saving throw when you cast this spell or be affected by it.
Both the rider and the mount are creatures, so they independently roll; both failed. Now, one of the potential effects on a d10 roll of 7 or 8 on upcoming turns is:
The creature uses its action to make a melee attack against a randomly determined creature within its reach. If there is no creature within its reach, the creature does nothing this turn.
It's not clear to me whether the rider would be confused enough to make a melee attack against its own mount.
Also, given the mount is not independent, it is not permitted to make an attack action, so I would assume it does nothing in my particular case, but I am curious about whether, in the case the mount were independent, it might attack its own rider.
Does a mount count as a "creature within its reach" of its rider? Is the rider a "creature within reach of a mount" if it is acting independently?