What is the correct way to use Disengage or Dash as a bonus action?

Question

We've been playing for a couple of years and this has been the usual playstyle of our Rogue:

• Move his speed (30ft) until in melee range of enemy
• Attack
• Disengage as bonus action, and move 30ft away from enemy without triggering opportunity attacks (OAs)

But, while reading a related question, I realized that Disengage doesn't grant you additional movement. It instead applies special traits to the movement you already have. Instead, the Rogue must do something like

• Disengage as bonus action (this can be done anywhere before the final movement part)
• Move half his speed (15ft) until in melee range of enemy
• Attack
• Move 15ft away from enemy without triggering OAs

What is the correct way to use Disengage as a bonus action?

What if our main actions are also a Disengage or a Dash? I'm guessing that

• Dash + Dash = Wasted action
• Disengage + Disengage = Wasted action
• Disengage + Dash = double speed without triggering OAs
• Dash + Disengage = double speed without triggering OAs

Is this interpretation correct?

Answer 1

It's almost correct

You can take multiple Dash actions, as many as you have available (whether by your action, bonus action, action surged action, Hasted action, etc). It has the effect of increasing your available movement on that turn by an amount equal to your Speed, and so they stack.

• Dash (A) + Dash (BA) = movement equal to thrice your speed

• Disengage (A) + Disengage (BA) = Wasted action

• Disengage (A) + Dash (BA) = double movement without triggering OAs

• Dash (A) + Disengage (BA) = double movement without triggering OAs

The difference between "speed" and "movement" is almost pedantic, but it is sometimes important. Your "speed" is the name of your statistic, normally determined by your race, and can be enhanced by spells, items, or feats. A human with the Mobile feat and Longstrider has a speed of 50ft.

"Movement" is the distance you have left that you may cover after subtracting all the distance you've already moved from your speed. So if you have used up 30ft of movement on a character with a speed of 50ft, you have movement left equal to 20ft.

Answer 2

Disengage does not grant additional movement, but Dash does (Emphasis mine).

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

This extra movement is added for each time you are able to take a Dash action, Action, Bonus Action, Hasted and so on makes no difference they stack additively.

So your rogue's "standard" round actions are incorrect. He could however do 15ft in attack, then Disengage followed by his remaining speed. See the section on breaking up movement in the PHB p190.

This assumes base movement of 30ft.

As for Dash your scenario that he likes to do would be 30ft in attack and 30ft out but incurring AOs, and the Disengage action affects all of your movement so taking two or more of those actions is redundant.

If you take the Disengage action, your movement doesn’t provoke opportunity attacks for the rest of the turn.

Answer 3

Dashing

A character can potentially dash more than once in a round. Each instance of the dash action increases the character's available movement for the turn by a value equal to their speed. Taking a dash action does not itself cause the character to move, it just lets him move further. (Movement is not an action.)

Theoretically, a (multi-classed) character could dash once as their normal action, a second time as bonus action via the Rogue's cunning action (or Monk's step of the wind), a third time via Fighter's action surge, and a fourth time via the haste spell. This would allow the character to move five times his normal speed (which is already doubled by haste), though you couldn't do much else.

Disengage

Disengage is an action (or bonus action via the Rogue's cunning action) that allows the character to move without provoking attacks of opportunity. That's all it does - prevents attacks of opportunity caused by moving. It doesn't grant any extra movement.

A character who uses his action to disengage cannot use his action for anything else on the same turn. He retains the ability to take eligible bonus actions, and as mentioned above, if he has some way to disengage as a bonus action, he can do whatever he'd normally be able to with his action.

Alternatives to Disengage

Among other effects, the Mobile feat allows you avoid attacks of opportunity for moving away from a character you've attacked (successfully or not). As long as he stays outside the reach of any character that he doesn't attack, he can move freely.

Sword Coast Adventurer's Guide and Xanathar's Guide to Everything includethe Swashbuckler Rogue archetype, which offers a similar ability via the fancy footwork ability. In a multi-class build, it's potentially more powerful as it doesn't specify attacks of opportunity caused by movement, just attacks of opportunity in general (relevant for things like Mage Slayer and Sentinel).