They have 1HP.
Similar to Eyebats, it hangs from the ceiling until it notices a player. After noticing a player, this monster will fly downwards until it hits the ground or the player and then explode, spawning 5 fireballs in all directions.
Each fireball deals 5 damage and does not set the player on fire. Try to hide behind terrain to avoid the fireballs. The Rogue and the Mage can easily deal with them by shooting them and freezing them, respectively.