The party at last confronts the Water Demon. A 12-foot tall monstrosity, the demon is a chimera of jellyfish, crab, eel, and deep-sea anglerfish, with a deranged human face on a telescoping neck, and a strange, red quartz crystal embedded in the center of its thorax.
The party fights magnificently, keeping on the move and protecting their casters while raining down blows on the demon, eventually shattering its protective outer carapace. Although its amorphous jellyfish underbody proves to be surprisingly resilient, a symphony of mace-blows, eldritch blasts, baleful songs, flaming spears, and bolthrower slugs finally take down the fell creature.
Noticing that its chest crystal floating in place, the party thinks quick and encloses it within the magical turquoise sphere they discovered earlier. The effect is immediate: a circular panel across the seam rotates a quarter turn, and the two halves seal together with a flash of radiant light.