Attacks that can Dismount a Rider. Any melee attack with a weapon of over 3 ft. in length that rolls a natural 20 will dismount a rider. Any melee attack by a pole arm of 10-ft. or longer will dismount a rider on a natural attack roll of 16 or higher (if the attack hits and does damage). If a mounted attacker is hit by a defender wielding a weapon with the dismount quality, the rider must make a Dexterity save vs. Petrify or be dismounted.
Dismounted. A rider that is dismounted falls prone and takes 1d6 damage (the GM may adjust for fast movement or very large mounts).
Morale. In most situations, mounted opponents vs. unmounted will represent an obviously superior force, triggering a morale check unless a strong leader on the side of the foot-soldiers is present.
Missile Weapon Use. Only trained riders can use missile weapons from horseback. Thrown weapons, short bows, composite short bows, and light crossbows may be used by riding characters at half their rate of fire. If used from a moving mount, penalties will apply: Less than ½ normal move: -1 to hit. From ½ to ¾ normal move: -3 to hit. From ¾ normal move to maximum speed: -5 to hit.
Rider Attack Bonus. Mounted combatants fighting creatures under 8-ft. tall on foot will gain a +1 “to hit” for height advantage.
Untrained Mounts. Mounts used in combat must be trained for such conditions. Otherwise, they will act normally based on the situation, ignoring the rider. If a mount flees, it moves directly away and if the rider attempts to control it, it will attempt to throw the rider. The rider must make a Dexterity save vs. Petrify or be dismounted (see below). A trained rider receives a +2 to this save.
Untrained Riders. Untrained riders cannot cause a mount to charge, cannot attack while mounted, and cannot control a panicked mount.
War horses. If ridden by a trained rider, a war horse in melee will fight starting on the second round as long as their rider stays mounted. Otherwise the mount will back out of melee and flee or, if being targeted by attacks, defend itself. As long as the rider is present, the war horse will attempt to stay nearby (but will avoid combat).
Any time a trained mount charges, the rider is considered charging as well (with regards to bonuses and penalties). While this means the mount cannot charge for 10 rounds, the rider can still charge (if not riding).
The trained mount can make an overbear or rush attack if directed by a trained rider.
The rider can attack while the mount moves through melee past opponents. While this can draw free attacks, the rider gains a +4 circumstance bonus on armor class against the free attacks (although if an attack misses by 4 or less it will instead hit the mount if the attack result would be a hit). All charging modifiers also apply to both rider and mount.
Mounts like horses require clear and (relatively) flat terrain to charge and require at least 50% of a normal movement rate in distance to charge with a rider.
If circumstances allow, the charging mount and rider, equipped with a long weapon (a lance of over 12-ft. in length) can attack foes on the periphery of a melee without threat of counter-attack if the foes are already in melee with other opponents (unless these opponents leave melee with their current foes).