Squidcreeper Sap is from a creature called a Squidcreeper that only exists in another world. Its sap is the only thing that can dissolve the glue that Balsam uses. It was need to remove Yovel's mask which Numnu had glued to his face as a prank. However the sap is so potent it could also dissolve Yovel's face if they weren't careful. Luckily they were able to remove his mask and Yovel kept his face.