Wraith

Wraith is a black ghost-like enemy with glowing, red eyes which only spawns in Hardmode. They have 200 health each and can travel through walls. Wraiths commonly spawn at the bottom of Corruption Chasms, 1-3 will also spawn when you smash a Demon Altar with the Pwnhammer. Wraiths will also spawn during Blood Moons, and are a severe hazard to the liveliness of your NPCs due to their ability to pass through walls. Due to the fact that Wraiths cannot pass through stone blocks, a Wraith-proof house would be lined with a perimeter of stone.