Am I allowed to double-dip on my mount's turn, granting it extra dashes?

Question

Here's a very silly situation that I'm sure would be easy to rule around, but as an exercise to understand the rules better, I'd still like to know how this works. It might even just be a variation of Can you move on your turn, and then use the Ready Action to move again on another creature's turn? (c.f. also the linked What are the basic limitations for using a Reaction to move? Does movement used on your Turn matter? for context)

Here are the steps I'm checking are possible:

0. Round zero
   • You are mounted on a controlled mount, and you share initiative.
   • You chose that the horse acts first (as per Jeremy Crawford's tweet)
   • As your action for the turn, you ready an action to dismount the horse when it finishes moving.
1. Round one
   • On the horses first turn in round one, you direct it to use the dash action (granting it an amount of extra movement, equal to its base speed) and then to move a distance equal to double its base speed
   • \$distance_{total} = movement_{base} + movement_{dash} = 2 \times speed_{mount}\$.
   • After the mount's movement is over your readied action triggers and you dismount
   • On your turn in round one, you take bonus actions/free interactions (basically, anything but an action) and no more than half your movement and remain within 5ft of the mount
   • You use the remaining half of your movement to mount the horse for the first time this turn.
   • When you mount it, you chose the mount to go after you in initiative order this time, and ready an action to dismount the horse as it finishes moving on it's next turn.
   • Mount round 1, turn 2 (😨), you direct it take the dash action, (granting it an amount of extra movement, equal to its speed) and move its speed again.
   • \$distance_{total} = movement_{base} + 2\times movement_{dash} = 3 \times speed_{mount}\$.
   • Other creatures get to act
2. Round two
   • On your next turn, you mount the horse and choose for it to come before you in initiative, thus acting before you in round 3.
   • Ready an action (as in turn 0) to dismount when the mount finishes moving in round 3.
   • Repeat the actions and movements taken in round 1.
   • (Optionally, if you interpret 'A controlled mount can move and act even on the turn that you mount it.' to mean the horse gets to 'move and act' on the same turn (i.e. your turn 1, round 2) then it gets to move again before round 3 comes around. This is not the standard interpretation.

In essence, if I do the above (or similar, accounting for any mistakes I've made in the explanation) can I double dip on my mounts extra movement by changing when in initiative order it goes, essentially granting it second turn and use of dash? It would be limited to only moving it's speed in a single round:

Every character and monster has a speed, which is the distance in feet that the character or monster can walk in 1 round.

However the Dash action grants extra movement (n.b., to be watertight, the quoted passage would have to say 'current round' not 'current turn', but the two words are used inconsistently, and the same interpretation would prevent dash ever granting extra movement for a round.)

When you take the Dash action, you gain extra movement for the current turn. The increase equals your speed, after applying any modifiers.

By the way, this isn't Does The Amazing Lightspeed Horse work, RAW? as I'm using readied actions to mount and dismount, but a similar question could be asked combining the two techniques.

Is this possible?

Answer 1

Each creature in combat only gets one turn, unless a feature explicitly grants a creature extra turns.

Further,

During a round, each participant in a battle takes a turn.

The general rule is that in each round, each participant gets to take a turn. One turn. If you have a creature taking two or more turns in a round without using a feature that explicitly allows them to do so (like time stop), then you have done something wrong. You conclude that your mount gets two turns in a round. This means you have done something wrong, and in your case, the thing you did wrong was change the initiative order after it has already been determined.

The order of combat is fixed once it has been determined.

The rules for "The Order of Combat" state:

The order of turns is determined at the beginning of a combat encounter, when everyone rolls initiative.

Once the initiative order is set, it is set for the duration of the combat. In your scenario, you are changing the initiative order in the middle of combat. The rules for initiative ties state:

If a tie occurs, the DM decides the order among tied DM-controlled creatures, and the players decide the order among their tied characters. The DM can decide the order if the tie is between a monster and a player character. Optionally, the DM can have the tied characters and monsters each roll a d20 to determine the order, highest roll going first.

So in round zero, there is a tie between your initiative and the mount's, and you resolve to let the mount go before you in the order. As the tie has been resolved, the order is now fixed unless a rule explicitly allows you to change the initiative order.

Answer 2

The effect of @Thomas Markov is right, but he got some of the reasoning wrong.

Mounted Combat changes initiative ordering

Mounted combat says:

The Initiative of a controlled mount changes to match yours when you mount it.

Specific rules beat general, so the order of initiative changes in the middle of your turn when you ride the mount.

Reorder turns doesn't change what has been done on that turn

Initiative determines the order of turns during combat.

During a round, each participant in a battle takes a turn.

If a turn is moved in the initiative order, it's still the same turn. If the mount moved half its movement speed earlier in the round on that same turn, it only has half it's movement speed left for that turn.

The DM may rule that the mount had to forgo its movement earlier for the round to continue

A no-fun DM may rule that the mount had to forgo any extra movements or actions for its turn to end so turns later in the order to happen, and this may be the absolute strictest RAW.

I'd rule, hopefully reasonably, that if your your turn gets moved later in the initiative order, you can pick up where you left off. This would allow for cool stunts (like you to ride a mount half its movement speed up to an ally, dismount, and then that ally to mount and use the rest of the movement speed of the mount) without breaking the basic action/movement economy.