David and the Midnight Unicorn

Twelve-year-old David Gonzales takes another trip to the lands below the drains in order to rescue his best friend Marty and their teacher. After a failed science experiment turns Marty into a unicorn and their teacher into a crowuzzle, both are forced through a painting portal that leads to the magical lands. Using his old teleporting hat, David goes down the bathtub drain. Instead of landing in Drainovia, rusty pipes send him to the Wuzzle Swamp.
Lost and in need of help, David only has three days to find his friends, get them changed back into humans, and return home. If he fails, they could be stuck forever in the Below Lands.