15.13 Ride
Mounts can be logistically challenging, though little of that complexity comes from the Ride skill itself. Characters without the Ride skill are unlikely to ride mounts into combat. On the other hand, characters trained in the Ride skill can generally ride mounts well within their skill level with no risk of randomly falling off. This means that Ride checks are rare in practice.
At higher levels, ordinary horses stop being a viable option in combat, both narratively and mechanically. Instead, you should provide players with the opportunity to use more level-appropriate mounts like unicorns. Be careful about introducing flying mounts, since flight introduces a great deal of complexity to the game.