Drop of Yen-Sorte's blood

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