Shadowflame Apparition

The Shadowflame Apparation is an enemy summoned by the Goblin Summoner during hardmode. Summoned in swarms as projectiles, they pass through blocks while attempting to ram the player. They are immune to knockback, and both they and their caster move very quickly, allowing them to easily swarm the player.

Trivia

 * An apparition is a name for a supernatural phenomenon, such as a ghost or phantom. Terraria incorrectly spells it as apparation.