Trained Mount

Light Armor Barding & Additional carry capacity (level 3)

The horse can now wear light Armor barding & carry an additional 54 Lbs.

After hours and hours of add-hoc training and failed attempts the horse will now wear light barding comfortably and without complaint. 

Medium Armor barding & Additional carry capacity (level 7)

The horse can now wear medium Armor barding & carry an additional 54 LBS

Over a period of time the horse has grown strong enough to wear heavier barding and carry more weight.

Heavy Armor barding, Additional carry capacity and Warhorse Combat experience (level 10)

The Horse can use heavy Armor Barding & carry an additional 54 LBS of carry capacity.

Trampling charge: the horse moves 20ft in a straight line at a target, the target must make a DC 14 strength saving throw or be knocked prone, if the target is knocked prone the horse can attack with a unarmed fighting melee attack as a bonus action.

Athletic Horse (level 15)

The horse adds half proficiency rounded up to any STR, DEX, or CON check it makes that doesn’t already use your proficiency bonus and when it makes a running long jump, the horse adds its strength modifier in feet to the distance.

Tenacious Horse (level 18)

At 18th level, the horse attains the pinnacle of resilience in battle. At the start of each of your turns, the horse regains hit points equal to 5 + its Constitution modifier if it has no more than half of its hit points left. the horse does not gain this benefit if it has 0 hit points.