Trampling Charge. If the horse moves at least 20 ft. straight toward a creature and then hits it with a hooves Attack on the same turn, that target must succeed on a DC 14 Strength saving throw or be knocked prone. If the target is prone, the horse can make another Attack with its hooves against it as a Bonus Action.
Mounting. Once during your move, you can mount this creature as long as it is within 5 feet of you or you may dismount if you are already mounted. Doing so costs an amount of movement equal to half your speed. For example, if your speed is 30 feet, you must spend 15 feet of movement to mount a horse. Therefore, you can’t mount it if you don’t have 15 feet of movement left or if your speed is 0. If an effect moves your mount against its will while you’re on it, you must succeed on a DC 10 Dexterity saving throw or fall off the mount, landing prone in a space within 5 feet of it. If you’re knocked prone while mounted, you must make the same saving throw. If your mount is knocked prone, you can use your reaction to dismount it as it falls and land on your feet. Otherwise, you are dismounted and fall prone in a space within 5 feet it.
While you’re mounted, you have two options. You can either control the mount or allow it to act independently. The initiative of a controlled mount changes to match yours when you mount it. It moves as you direct it, and a controlled mount can move and act even on the turn that you mount it. If the mount provokes an opportunity attack while you’re on it, the attacker can target you or the mount.
When mounting a mount, you occupy the center-most space in the creature’s space. if the center of the creature’s space is an intersection, you occupy all spaces which touch that intersection. This means that a human on a horse occupies the mount’s entire space.