Crimson Helmet

The bonus is passive healing that builds. Go without taking a hit and the faint red pulses around your character come faster, each one another point of health returned, and standing still speeds that up. That makes it a set for the time between fights more than the fights themselves. It closes the gap after a rough cave dive without a potion. You also trail red bubbles while moving, pure decoration.

This is the crimson half of a pair, and the corruption set solves a different problem. Shadow armor gives movement speed, which helps you avoid damage in the first place. This one gives recovery after you take it. Ore does not cross between world types, so you wear whichever your world grew.

The bonus needs all three pieces, so wearing it means fighting in weaker protection than the alternatives. The way around that is to park it on a second loadout, switch over only while you are safe and topping off, then switch back before the next fight. Get caught mid swap and the exposure is real. A Band of Regeneration, or a Shiny Stone later, stacks with it and makes the parked healing worth the trip.