D&D 5E Rules question - Dissonant Whispers movement with Warcaster on OA

[ECMO3]

So if you have the warcaster feat and cast dissonant whispers when someone moves away from you:

"On a failed save, it takes 3d6 psychic damage and must immediately use its reaction, if available, to move as far as its speed allows away from you."

So if I cast DW and it fails its save how does the movement come into play with respect to the normal movement he gets on his turn? Does it use the normal movement or does he get extra movement to use with this reaction?

For example the BBEG with a move of 30 is right next to me. He leave my reach to move towards my ally who is 15 feet away. Once he gets more than 5 feet I cast DW and he fails his save. So he has already moved 5, does this mean:

1. he uses his reaction and moves 25 more (moving past my ally and getting an AO from him as well) using all his movement and effectively being stuck having no more movement left at that point unless he takes a dash action.

OR

2. The spell gives him an extra 30 to move on his turn so he moves 30 more (now 35 feet away from me), again causing an OA from my ally, but then he can use the rest of his normal movement to move another 25 feet, enough to move back towards my ally and attack him like he originally intended.

 

[ninjayeti]

RAW the forced movement comes from their reaction, and does not use any of the creature's regular movement. I don't see any other rule which would change this just because the reaction occurs during their normal movement.

So #2.

 

[Neonchameleon]

The spell no more takes up his base movement than the Dash action takes up someone's base movement so #2. It's still a really good spell.