Flint

Hold the attack button and it winds up. Let go and it sweeps a wide arc around you, trailed by a yellow aura that reaches past the blade itself and covers the ground behind you as well, so it is not the forward only swing the animation suggests. Hold long enough for the head to brighten and start humming and you have a full charge, and that release also sends a line of fire running along the ground ahead of you.

It stops dealing damage after two separate targets, which is why the charged wave rather than the swing itself is the actual weapon. The arc will not grow: size modifiers and a Titan Glove do nothing for its reach. Melee speed bonuses do not make it swing any faster either, although attack speed modifiers on the weapon itself do, and neither touches the charge time. Legendary is the best modifier.

• It needs a surface. The game looks a short way down from a point just in front of you for a floor or platform to build on, and if it finds nothing, nothing spawns. Swinging out over a chasm gives you the swing alone.
• If you are standing inside a solid block it searches upward instead and lays the wave above you, so tight tunnels usually still work.
• The pillars climb over obstacles and cut through terrain when they need to, but a drop deeper than a short step ends the run. Flat or gently rolling ground gives it the most distance.
• Under reversed gravity it forms along the ceiling and travels the same way, which is fine once you expect it.
• Later pillars stand taller than the first ones, so the far end of the wave covers more vertical space than the near end.

The wave is a row of separate fire pillars, and each one carries its own hit timer, so they never step on each other's damage. A segmented enemy driving straight down the line eats pillar after pillar from one release. World Feeders, Wyverns and even The Destroyer take enormous damage from a single well timed swing as they close on you. Time it for the moment the head of the worm is coming at you head on.

The weapon is part of a crossover with Dead Cells. The former prison warden the tooltip refers to is the Concierge, that game's first real boss, and the line itself is a rework of the Flint's flavor text over there.