The energy stored inside them was consumed to instantly conjure the spells while also extending their area of effect to the area encircled by the feathers. The black ones combined with the blue feathers to form the tier five spell, Ice Coffin.
A swarm of black crystal daggers filled the air, each one of them enveloped in a frost aura so cold that it started to snow. It wasn't their razor-sharp edge nor the darkness energy they carried to make them lethal so much as their ability to stick to their target.
Dodging them all was impossible and once one of the daggers hit, the frost aura would fuse the ice crystal to its victim's flesh. The cold would suck away the heat just like the darkness imbued within ate at the life force, leaving the target of the spell no way out.