Drop of Yen-Sorte's blood
The drop of Yen-Sorte's blood is an artefact offered for 7 Mayan crowns in the Shop of Wonders in Delos. This smooth, warm, crystalline droplet resembles a ruby, and refracted all ambient light in such a way that it even glows a little bit. This drop of blood, consumed on use, grants the owner base-level mastery in every publicly-known weapon proficiency.