Reactive Equine Vault

During another creature or player's turn, if that creature or player fails an Athletics or Acrobatics check or is falling from a height of 15ft. or more while within 40ft. of you but no closer than 10ft. of you, as a reaction you can choose to gallop towards the target and vault with your strong equine biology to catch or rescue it from the failed check or potential fall damage, so long as it is the same size category as you or smaller. You and the target land 10ft. behind the target's initial location when taking this reaction.

While galloping and vaulting, hostile creatures or players can take opportunity attacks as a reaction as you pass them by.

If the target is a smaller size category than you, you may choose to catch them on your back instead of with your arms. A player that demounts you afterwards expends half their movement points for the turn in doing so. A creature demounting you afterwards expends an action and all their movement points for the turn in doing so. 

You can only do this once per round during a combat encounter. Otherwise, you can do this as many times as you'd like outside of combat.