It is strangley a purple-pink color near the top, but more dark blue near the bottom. A strange man whose name is Charold will offer to take you across the river for four coins. Though the river is swimmable, it is sometimes best to do this and avoid the underhands in the river. The river is based on the River Styx from Greek mythology. Also, the Underhands are based on the souls that pulled Mario into the river. Charold, the man who takes Mario across the river, is based on Charon, the man who ferried the souls across River Styx.
Mario must head down into the River Twygz after obtaining the key from Queen Jaydes. At the bottom, Mario must flip to find a secret hole that leads down to a locked door which the key can be used to unlock. Afterwards, Mario has to navigate though the sewage-like system until he reaches another door. After hopping up the fountain, Mario reunites with Luigi who decides to join him on his quest.