For the duration you unleash a freezing aura. Creatures that start their turn within 20 feet of you must succeed a Constitution saving throw, or take 2d8 cold damage and have their speed reduced to 0 until the start of their next turn. Creatures that succeed their saving throw take half as much damage and their speed is reduced by half. As a bonus action on each of your turns for the duration of the spell, you can actively control the aura, excluding a number of creatures in the area up to your spellcasting modifier from the effect of the spell until the end of your next turn.