From the Super Mario Wiki
Torrential Maze is stage 2-4 of the game Yoshi's Story. The level is composed of a labyrinth of water, and is flooded with spikes, jelly, and extremely fast moving water. Enemies include Spiked Fun Guy and Vine Slime. It seems to be part of Jelly Pipe because of its background and the fact that jelly exists there. Black Yoshi can be found in the level.
To avoid a dark scary cave, the Yoshis entered a nearby tunnel. Inside they found a maze that overflowed with rushing water. Perhaps they should have just gone through the cave instead!
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