Dark matter
Dark Matter is an obstacle in Super Mario Galaxy, and its sequel Super Mario Galaxy 2, which appears in Bowser's Dark Matter Plant. It can be found in patches, and has a swirly, purple and black appearance to it.
Bowser was generating Dark Matter at his Dark Matter Plant in order to destroy the whole galaxy in order to create his new one. If Mario or Luigi touch any Dark Matter, they will disintegrate and lose a life. Dark Matter can also burn holes in the ground that will make Mario or Luigi lose a life should they fall into one.
In its sequel, they are found rarely in the game. One of its appearances was the Daredevil Run for Bowser Jr.'s Boom Bunker. A Dry Bones-like enemy has Dark Matter stuffed in its mouth and eats the regenerating floor away. That enemy is known as Mattermouths.
