The good ship Melancoly Annie has developed a sudden -perfectly square- hole in the hull. A burn mark around the outside of it.
On the Thark side of the river, there is a square hole leading into the sewers.... hmmm
orcs, mushroom men, and a great room with a bullywug making a castle out of a huge gelatinous cube! He was using his slimy nature to make a coating on the inside of the cube and make it big enough to use as a home/armor.
It's surprising how quickly the gelatinous cube exploded... Just the right magic item for the job.