Ready Action to intercept enemy?

Quote from Plaguescarred >>

Quote from SmiteMakesRight_3_5 >>

Quote from Plaguescarred >>

In theory, it can still be usesul on that same turn a creature Ready the Dash action, if it was able to move somehow without using its own Reaction, it could potentially gain the extra movement. For example, an Adult Black Dragon could upon taking its Legendary Action: Pounce following a readied Dash then moves up to 60 feet.

I suppose that would work as long as you trigger the Dash first.

 Why so? Typically, you deduct the distance of each part of your move from it until it is used up or until you are done moving, so i believe the effect of the Dash action can happen at any time on the turn so long as you aren't done moving i guess. Don't you agree?

Yes and no.

First, I read the Pounce action more closely and Dash doesn't affect it. Dash increases your movement (a resource you normally have on your turn). Second, Pounce explicitly says the Dragon moves up their Speed. Dash doesn't change Speed and therefore doesn't affect Pounce. As an aside, the action is after another creature's turn so technically, they are in a between turns limbo. There may be some weird rules interactions with that timing that I can't think of right now. I think there was a third party or homebrew feature that gave a reaction on every creature's turn for use with that feature, but if that exists, it's off topic for this discussion.

Second, you don't have to Dash before you move, but if your Speed is 30, you have to Dash before you move that 31st through 60th foot. In the case of the Pounce, if they worked together, you fully move and attack within the Pounce, so the Dash re/action has to come first.

To me there's no in-between turns per se meaning it's always a creature's turn in Initiative order. So Legendary Actions take place after another creature’s turn ends yet before the start of the next creature's turn. So i usually have it occur while it's still the current turn ending, otherwise going one-on-one against legendary creatures would mean they can't use them.

As posted below, movement can be done off turn when a game feature specifically let you move this way.

Dash: When you take the Dash action, you gain extra movement for the current turn.

Inspiring Movement: When an enemy you can see ends its turn within 5 feet of you, you can take a Reaction and expend one use of your Bardic Inspiration to move up to half your Speed. Then one ally of your choice within 30 feet of you can also move up to half their Speed using their Reaction. None of this feature's movement provokes Opportunity Attacks.

Relentless Avenger: Your supernatural focus helps you close off a foe's retreat. When you hit a creature with an Opportunity Attack, you can reduce the creature's Speed to 0 until the end of the current turn. You can then move up to half your Speed as part of the same Reaction. This movement doesn't provoke Opportunity Attacks.

Quote from Plaguescarred >>

To me there's no in-between turns per se meaning it's always a creature's turn in Initiative order. So Legendary Actions take place after another creature’s turn ends yet before the start of the next creature's turn. So i usually have it occur while it's still the current turn ending, otherwise going one-on-one against legendary creatures would mean they can't use them. [...]

 This is also how I'm ruling it. A Legendary Action happens outside the monster's turn, after another creature's turn ends, but it doesn't create a separate turn.

Quote from Plaguescarred>>

To me there's no in-between turns per se meaning it's always a creature's turn in Initiative order. So Legendary Actions take place after another creature’s turn ends yet before the start of the next creature's turn. So i usually have it occur while it's still the current turn ending, otherwise going one-on-one against legendary creatures would mean they can't use them.

With that ruling, then the Reaction for the Held Dash action must be taken before the Legendary Action in order for it to affect the Legendary action's movement.

Quote from Plaguescarred >>

As posted below, movement can be done off turn when a game feature specifically let you move this way.

Dash: When you take the Dash action, you gain extra movement for the current turn.

Inspiring Movement: When an enemy you can see ends its turn within 5 feet of you, you can take a Reaction and expend one use of your Bardic Inspiration to move up to half your Speed. Then one ally of your choice within 30 feet of you can also move up to half their Speed using their Reaction. None of this feature's movement provokes Opportunity Attacks.

Relentless Avenger: Your supernatural focus helps you close off a foe's retreat. When you hit a creature with an Opportunity Attack, you can reduce the creature's Speed to 0 until the end of the current turn. You can then move up to half your Speed as part of the same Reaction. This movement doesn't provoke Opportunity Attacks.

The problem with these examples is that in order to move, you have to expend your Reaction and thus don't have the Reaction available for a held Dash. The Legendary Action resource, if you rule that it is part of the same turn, is the only practical example of movement + Dashing off turn.

I know, it's the reason why i brought up Legendary Action: Pounce  as one way to move somehow without using your own Reaction. 

These examples are not compatible with scenario where you Ready the Dash action, i put them only to demonstrate that off-turn movement is still movement which Dash gives you in extra when taken.

Quote from Plaguescarred >>

These examples are not compatible with scenario where you Ready the Dash action, i put them only to demonstrate that off-turn movement is still movement which Dash gives you in extra when taken.

Yes, but the Combat Turn rules say you can move up to your speed on your turn. The Reactions you quoted also say the same thing; you can move up to your speed. Others will say half speed or something. Dash increases your movement but does not actually give you the ability to use it. In 95% of the cases, if you want readying a Dash to work, you should just ready movement instead and are thinking Dash would give you double speed to move instead.