The Bloody Worm Scarf is a craftable Hardmode, Expert Mode-exclusive accessory that provides a 10% increase to damage reduction and increases melee damage and speed by 10%. This accessory can be considered the Crimson counterpart to the Amalgamated Brain, even though they both can be crafted regardless of the world evil.
If the player lives in a Crimson world, defeating the Brain of Cthulhu will make the Dryad sell the Worm Scarf.
If the player lives in a Corruption world, defeating The Hive Mind will make the Dryad sell the Bloody Worm Tooth.
The damage reduction also stacks with the Worm Scarf.
While the Amalgamated Brain is geared towards all users, the Bloody Worm Scarf is geared primarily towards melee users, as it increases damage for melee weapons.