What is Shadow used for in Hades 2?

You unlock it at the same time as you unlock the Shadow Extraction recipe.

That’s all you better know to get to create Shadow for your incantations in Hades 2.

Melinoe casts an incantation at her cauldron in Hades 2.

The Alchemy tab of the cauldron in Hades 2, with the Shadow Extraction recipe highlighted.