|Located:||Near an abandoned castle|
|First Appearance:||And then there was Nox Decious|
The dark forest is a sinister forest where evil forces tend to dwell. There is a clearing which contains an abandoned castle. It is where Mario, Luigi, and their best friends encounter Nox Decious for the first time and where Mario ultimately fights Mr. L.
1,000 years ago, Arthur's knight Sir Tristian fought Nox Decious in this very spot. The castle was in ruins then as well, so it is unknown when it was still functioning as a castle. Thousands of years ago, the castle belonged to Merlin and Nox Decious, but once he had turned evil, Decious has destroyed the castle leaving it nothing more than a mere wall.
Mario, Luigi, Peach, Link, Ash, Donkey Kong and Brock travel to the abandoned castle in order to face Decious (though Ash ditches the group to catch "Chicken Pokemon"). Decious arrives the face them, but despite their best efforts, he easily overpowers the group. Before departing, Decious mocks Mario and declares that Bowser and Ganondorf bow to him, not vica-versa as Mario and his friends had previously thought. It later transpires in Season Five that both Decious and Bowser are in Ganondorf's service, and Decious' claim to the contrary was a lie he told in an attempt to demoralize Mario.
Mario and Denise visit the castle on the search for the Blue Hood, Mario explains how the wall was a great castle. When Mario was young he was told a detail from a story, Denise asked what it was, but then they were confronted by the blue hood.