Challenge Node

Not to be confused with Challenge Mode.

The Challenge Node.

“Have you two come to test your limits in the Challenge Node?”

—Emoglobin, Mario and Luigi: Bowser's Inside Story

The Challenge Node is an area found inside Bowser's body in Mario & Luigi: Bowser's Inside Story that is, apparently, located in Bowser's spleen. This area is completely optional and does not need to be entered to complete the game.

Challenges

Here, Mario and Luigi can participate in several challenges:

• The Gauntlet - Here, the Mario brothers can fight X Bosses, which are optional bosses that are similar to bosses they have fought before, but more tough. One of these bosses, Bowser X, is the toughest boss in the game.
• Cholesteroad - Here, Mario and Luigi use the Special Attacks they have learned to fight the same enemies until the player messes up.

There is also a block that works the same way a Rally Block does here. If it is hit 99 times in a row, the player can double their Coins whenever they want, but only once.