The Dissonant Whispers spell description (PHB, p. 234) states:
The target must make a Wisdom saving throw. 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.
The War Caster feat (PHB, p. 170) states:
When a hostile creature’s movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.
If the creature failing the Wisdom saving throw from Dissonant Whispers moves past another character provoking an opportunity attack (as per this Q&A), and that character also has the War Caster feat; then they also cast Dissonant Whispers as an opportunity attack using the War Caster feat (and the creature also fails the Wisdom saving throw) what happens? Since the creature is already using their reaction to move:
- does it have no effect, or
- do they then move their speed minus the distance already moved from the previous Dissonant Whispers?