Mounted Combat Rules
If an animal is being used as a mount, companion or otherwise, it will act according to the mount rules. Without a rider to guide it, a mount avoids combat. Meaning, if you are out of the saddle and not actively commanding it, it will only participate in a fight to defend itself. The exception is if the animal is trained to Defend. In that case, it will stand its ground and also defend the fallen rider.
I assume that combat mounts have the General Purpose of Combat Training. This means that the mount knows the following 6 tricks requiring a DC 10 Handle Animal check (DC 12 if the animal is injured) to execute :
Attack – The animal attacks apparent enemies. You may point to a particular creature that you wish the animal to attack, and it will comply if able. Normally, an animal will attack only humanoids, monstrous humanoids, or other animals. Teaching an animal to attack all creatures (including such unnatural creatures as undead and aberrations) counts as two tricks. (This can be purchased with an animal companion’s extra tricks.)
Come -The animal comes to you, even if it normally would not do so.
Defend – The animal defends you (or is ready to defend you if no threat is present), even without any command being given. Alternatively, you can command the animal to defend another specific character.
Down – The animal breaks off from combat or otherwise backs down. An animal that doesn’t know this trick continues to fight until it must flee (due to injury, afear effect, or the like) or its opponent is defeated.
Guard – The animal stays in place and prevents others from approaching.
Heel – The animal follows you closely, even to places where it normally wouldn’t go.
According to the Ride skill, some checks are required to ride a mount in combat.
Guide with Knees: You can guide your mount with your knees so you can use both hands in combat. Make your Ride check at the start of your turn. If you fail, you can use only one hand this round because you need to use the other to control your mount. This does not take an action. DC 5
Fight with a Combat-Trained Mount: If you direct your wartrained mount to attack in battle, you can still make your own attack or attacks normally. This usage is a free action. DC 10
To fight from the back of a combat trained mount with a two-handed weapon, expecting both you and the mount to attack, requires a DC 5 Ride check (Knees), a DC 10 Handle Animal check (command mount to attack) and a DC 10 Ride check (mount and you both able to attack) each round.
Mounted combat things to remember:
When you attack a creature smaller than your mount that is on foot, you get the +1 bonus on melee attacks for being on higher ground.
If your mount moves more than 5 feet, you can only make a single melee attack.
If your mount charges, you also take the AC penalty associated with a charge. If you make an attack at the end of the charge, you receive the bonus gained from the charge.
You can use ranged weapons while your mount is taking a double move, but at a –4 penalty on the attack roll. You can use ranged weapons while your mount is running (quadruple speed) at a –8 penalty. You can make a full attack with a ranged weapon while your mount is moving.
Handling an animal is a move action, while “pushing” an animal is a full-round action. (A druid
or ranger can handle an animal companion as a free action or push it as a move action.)