During the events of Mario & Luigi: Partners in Time, the four Mario Bros. (Mario, Luigi, Baby Mario and Baby Luigi) traveled to the Toadwood Forest of the past in their effort to locate shards of the Cobalt Star. However, instead of finding a piece of the Cobalt Star, the brothers discovered the bodies of lifeless Toads strapped to the forest's trees.
The evil extraterrestrials known as the Shroobs had genetically-engineered the trees in the forest for a particularly malicious purpose. During the Shroob invasion, Toads would be abducted and placed in these trees. The trees would then proceed to drain the vim, the Toads' life force, out of the fungus folk, slowly killing them in the process. The vim was then transferred through the roots of the trees to the Vim Factory, a huge Shroob-created building built in the middle of the Toadwood Forest. Once there, the vim would be altered with chemicals and be used as fuel for the Shroob UFOs.
As the four Mario brothers journeyed through the forest, they encountered multiple lifeless Toad bodies strapped to the vim-sucking trees. One Toad, Toadiko, managed to gather enough strength to reveal the Shroobs' plans to the Mario brothers. Unfortunately, Toadiko was caught and turned into a purple mushroom by the Shroobs. However, the Mario brothers of past and present managed to escape the Shroobs' wrath. Eventually, the Mario brothers discovered the factory in the heart of Toadwood Forest, unlocked the front door, and proceeded into the place of darkness.
The Mario brothers also investigated the many hollow tree stumps found throughout Toadwood Forest. To enter these tree stumps, Mario and Luigi had to throw Baby Mario and Baby Luigi over their heads and into the stumps. Usually, the baby Mario brothers would find coins, mushrooms, and even badges. However, sometimes monsters would make their home in a tree stump and would engage the babies in battle when the toddlers entered their territory.
While the Toadwood Forest is particularly creepy, only Luigi show signs of actually being scared. Even Baby Luigi remains controlled in the scary forest, indicating that Luigi's current fears were not present when he was a baby.
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