A prepared potion Mordecai believes will probably stop Shi Maria's unnaturally sticky web from bonding to the drinker.
Shi Maria's web sticks tightly on contact even though the real spider species inspiring it does not normally use adhesive silk. Mordecai prepares an anti-adhesive potion as one of several ways to cross.
His confidence is only qualified as probable, so Carl refuses to test it while other reliable options exist. The party instead uses Magic Missile, fire susceptibility, and negotiation to remain outside the web field.
A slick alchemical vial whose contents bead away from a strand of white spider silk.
The potion is an unverified emergency countermeasure for the spider's terrain control.