Burning Sphere

Nothing spawns this on its own. Fire Imps throw it, three in a row, then blink somewhere else and throw three more, which is why an imp fight feels like it is arriving from every angle at once. They live in the Underworld, mostly around the ruined houses, so this is the projectile you meet on your first hellstone run.

Each sphere travels in a flat line at a steady pace and goes clean through terrain, so ducking behind a rock buys you nothing. What it will not do is survive a hit. The game files count it as an enemy rather than a projectile, so it has health and dies to anything that deals damage, a pickaxe swing included. In a tight corridor it is usually faster to shoot the volley down than to weave through it. Letting one land will often set you on fire, and taking a burn down there while you are already negotiating lava is how a routine trip turns into a retreat.

• Being filed as an enemy is also why the imp's banner affects it and why it shows up with a stat line at all.