Does teleporting off of a mount count as "dismounting" the mount?

Question

The Question

Is "dismount" in the first sentence of the first paragraph on "Mounting and Unmounting" section of the rules using the generalized meaning of "dismount" found elsewhere in the rules, or referring to the specific mundane method of dismounting a creature specified in the subsequent sentence?

Mounting and Unmounting And Related Rules

The PHB states

Once during your turn, you can mount <...> or dismount. Doing so costs <..>"

If you dismount a mount, you cannot normally mount a new one. This is a well known limitation that prevents a variety of abuse cases when combined with the rule

A controlled mount can move and act even on the turn that you mount it.

to prevent characters from getting excessive amounts of movement by using multiple mounts in one turn (especially cavaliers who only spend 5 ft of movement to mount or dismount). See Can I move 240' and attack in one round by using two riding horses? for a more direct discussion of the mundane case.

Does this limitation only apply when you dismount using the rules provided in the Mounted Combat section of the PHB (by using some of your movement)? Or does the once per turn limitation on dismounting/mounting a mount apply to any method of going from the "mounted" to "unmounted" state? I was hoping to find an answer at How does the Misty Step spell interact with a mount? but it only covered whether the mount teleports with the rider.

If you cast a spell like Misty Step, use a racial feature like Shadar-kai teleportation, or a class feature like Monk's Shadow Step and teleport so that you are no longer on your horse, could you mount a new horse in the same turn, or remount the same one?

Part of my confusion comes from the general usage of the word "dismount" in other areas. For example later in the rules for "Mounting and Dismounting" it states

If your mount is knocked prone <...> you are dismounted and fall prone.

and magic item Saddle of the Cavalier has as part of its effect:

You can't be dismounted against your will

which suggests that being removed from a mount by any means is considered "dismounting" in at least some cases. "Dismounting" in these cases is obviously not referring to only hopping off of the horse willingly with your own movement.

However making a blanket ruling that "anything that makes you no longer mounted counts as dismounting" becomes problematic in its own way. I really don't think Saddle of the Cavalier should prevent a rider from being affected by Banishment (because it "dismounts" them) for example.

Example Situations

Teleportating dismounts + mundane remounts could be useful in a number of uncommon cases but not extremely contrived cases:

1. Switching horses or mounts could be accomplished in a single turn, potentially allowing a character to move incredible distances on a prepared escape route:
   • Begin the turn mounted on a Riding Horse you don't mind leaving behind
   • Have mount take Dash action and move double that mount's speed (120 ft)
   • Misty step away from that mount (moving 30 more feet)
   • Take Dash action yourself (move 30 feet)
   • Move half your normal movement (15 feet)
   • Mount a strategically placed getaway mount (second riding horse)
   • Have mount take Dash action and move double that mount's speed (120 ft)
   • The total net benefit (compared to not mounting a new mount but using all the same other resources) is 105 extra feet, plus beginning the next round mounted.
2. Melee character with Mounted Combatant working around positioning issues.
   • Begin the turn mounted.
   • Mount is unwilling or unable to move closer to enemy. Either an intelligent mount that already acted, or a controlled mount that's Frightened/Restrained/Paralyzed/Charmed/etc.
   • Misty Step to enemy (preferably the one causing your mount's distress)
   • Attack Enemy, preferably killing them so you don't deal with Attacks of Opportunity and can end the condition (if any) on your mount.
   • Walk back to your mount (up to half your movement)
   • Mount using his movement so he's able to provide defensive benefits to his mount, and continue combat normally the next round.

Answer 1

Dismounting only costs speed as part of your move

Once during your move, you can mount a creature that is within 5 feet of you or dismount. Doing so costs an amount of movement equal to half your speed.

If you chose to dismount your horse during your move, doing so will cost you half of your speed. If you are thrown off your horse, or leave it some other way, it does not. For example

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.

In these cases, dismounting does not cost you half of your speed, as you are not doing it during your move, you are doing it as a reaction or as a result of being knocked prone. Likewise, when you teleport away from your horse, you are not doing it as part of your move. You are doing it as part of some action that teleports you, like casting misty step. So it does not cost you half of your speed.

You can teleport off your horse, move half your move, and re-mount it, or mount another horse. Both your examples work.

Note that the DM might rule that if you teleport from a sitting position, you end up in a sitting position. If teleporting and falling 5 feet can be used to counter a prone condition is contested. If the DM rules you end up sitting or prone on the floor after teleport from being mounted, then teleporting would not cost your speed, but standing up from there to continue moving would cost you half your speed.

Answer 2

You can teleport OFF your mount freely; Teleportation doesn't count as movement.

This premise is why you can misty step away from an enemy without provoking an attack of opportunity. Teleporting doesn't count as movement. If teleporting off your mount isn't movement, and dismounting involves movement, you haven't "dismounted" this turn.

Whether or not you can teleport onto a mount and be mounted in the same teleport action is a different question in terms of action economy and movement rules, and you'll need your DM's input on that. I don't believe there's a RAW answer for such, since mounting requires movement.

I'd personally allow it and just require half your movement after - which means that you'd have to have at least half your move left after the teleport to pull this off (you can move as part of other actions, so this seems the most likely RAW version of what you're seeking IMO).

But teleporting off your mount, then remounting it (or another) normally with movement, should be totally fine.