A Desert Spirit's Curse, the projectile fired by Desert Spirits.
Desert Spirits have an attack pattern that is unique compared to most enemies. Upon appearing near a player, they will cast a single, colored projectile that attempts to home in on the nearest player, phasing through blocks and slowly gaining speed. After a certain amount of time, it will duplicate and explode. Similar to other casters, it will then teleport to a different location and repeat the process. It
should be noted that the projectiles themselves do not deal any damage, but their explosions do.
The Bestiary entry for the Desert Spirit: "Ancient magicks corrupted the minds of the once friendly desert djinns, releasing them full of hostility from their lamps."