Ice Sickle

Each swing throws a spinning blade that slows as it travels, so it ends up hanging in the air a short distance ahead of you before it fades. Anything that walks into that hovering blade takes a hit and gets knocked back out of it. Used well, it is a barrier you put between yourself and whatever is coming, and the sword swing itself is almost incidental.

A projectile that pierces several targets and then sits in place is close to ideal against anything segmented. Park one across the path of the Destroyer, a Digger or a Dune Splicer and the body drags itself through the blade section by section. Against single large targets it is far less impressive, since each throw only lands once.

Faster swings also throw the blades harder, which pushes them out further before they stall. Speed accessories and prefixes buy you both rate of fire and reach here, which is not true of most swords.

The frozen underground in hardmode, off several of the tougher ice enemies. None of them drop it often, so treat it as a bonus for time already spent mining down there rather than a farm worth setting up on purpose.