Knightfall
World of Kulan DM
Reminder: The Earth Elemental was summoned by Caerth.
D&D Wiki said:Once free, the creature can move (including flying) at half speed. A character capable of spellcasting who is bound by the goo must make a DC 15 Concentration check to cast a spell. The goo becomes brittle and fragile after 2d4 rounds, cracking apart and losing its effectiveness. An application of universal solvent to a stuck creature dissolves the alchemical goo immediately.