The Shroom Game is a minigame hosted by a gnome in Neverwonder.
When tapped on, the gnome activates the four mushrooms (green, red, yellow and blue), which will glow in a random order. When they're done glowing, the player has to tap the mushrooms in the order that they glowed.
The first time the Shroom Game is played, the mushrooms will glow a total of four times. Every next 'level', the mushrooms will repeat the previous glowing order before an additional mushroom glows for another time. If the player successfully taps on the mushrooms in the correct order, the gnome will award gold equal to 10 times the times the mushrooms glowed (so the first level awards 40 gold, the next 50, and so on). If the player fails, the game is reset back to level 1, with a new glowing order and any gold awarded for levels previously completed not given again.
In addition, the player CANNOT play the game before the first wave or when the battle is paused. That means that the player will have to memorize the order while managing his or her towers and spells to defend against enemies.
On the bright side, no official maximum has been confirmed yet, so players can theoretically play the Shroom Game infinitely many times and, if they are quick enough, use the gold earned to build their dream setup on the level.