Soul Fragment

The  is one of two types of material needed to craft the Soul Whip and Eternal Hoof respectively. It's dropped from killing the Grim Reaper, with a Guaranteed(100%) chance to get it on each kill.

This item is available in three-hour windows every Spooky Festival, more specifically when the Fear Mongerer is available in the hub. It's only recommended to fish for s at a Fishing level of 26 or higher, as that's the minimum level needed to fish up a Grim Reaper.

Trivia

 * The texture for this item is based off of obsidian blocks from Terraria.