Lesser blue mutagen is an alchemy ingredient and is be used to craft Blue mutagens. They can also be used to augment abilities, but are not as effective as their regular or greater counterparts. When placed in the diamond-shaped slot in the character panel, they give +5% to sign intensity, which increases by 5 up to a max of +20% if all 3 skills attached to it are blue.
Blood and Wine expansion
With Blood and Wine, the player can now craft these with other ingredients.