Our group got attacked by creatures under the same haste spell. Our caster responded by casting slow on them but due to their spreading out was unable to hit all the ones under the effects of haste, and also hit some that were not under the effect of haste.
Slow counters and dispels haste.
Haste dispels and counters slow.
We were unclear on exactly what happens. We came up with the following potential cases and were not sure which was correct
- The whole haste spell is dispelled and no other effect
- Haste is dispelled and others can be affected by slow
- Only the ones within the slow area are dispelled of haste or slowed
There is a related question which was dispel magic and multiple summons from the same spell.