Syphon Time

Up to six creatures of your choice in a 40-foot cube within range must succeed on a Wisdom saving throw or be affected as if by the slow spell for the duration. For each creature who fails their saving throw and is slowed, choose a different creature that you can see within 30 feet of you to be affected as if by the haste spell.

Whenever the spell would end on a slowed creature, the spell also ends on a hasted creature of your choice. Creatures hasted by this spell do not suffer the usual wave of lethargy when the spell ends. Dispel magic and similar spells or abilities can only end this haste effect by ending the spell on a slowed creature.