Mind Matter is a particularly powerful manifestation of Dark Matter, being able to control the minds and sanity of those around it. It first appeared in Kirby: Onslaught as a main villain, commanding the Demoninc forces which attacked an array of planets.
Mind Matter came into existence in the antiquity of the Shiver Star. A fusion of Dark Matter and Human insanity, it sought to create minions for his master. Dark Matter NEVER had employed free willed minions before, and the idea, being Mind Matter, was supposed to cover Dark Matter's weakness of not being able to easily extend into areas without succeptable life forms. The Humans, being ignorant, very succeptable, and on the planet of his birth, would make perfect minions. Mind Matter began slowly molding Humans into the perfect race - destructive, greedy, and completely devoted to Dark Matter. It all seemed to go so well for the first millenia and a half. However, something went terribly wrong.
The Failing of the Plan
Humans became TOO chaotic. They became so chaotic and destructive that even Mind Matter itself feared them. Thus, it decided that it must exterminate the Human race, and used the most powerful Human sect to initiate a great war. Mind Matter then set off to find another race for his plans.
A New Race
Mind Matter came across a new planet, shaped like a heart - the Ripple Star. The denizens of this planet were very peaceful and friendly, and possessed a very powerful artifact. Mind Matter liked what it saw, and decided it would now use the Fairies as his new pet project. However, the they were more resistant to Dark Matter, and put up a fight. With the Fairies and their Crystal on one side, and Mind Matter, Dark Matter, and a league of twisted Fairies bent on power on the other, this was probably the only war in Fairy history. The Fairies won, and thus Mind Matter left along with its corrupted Fairies, who showed signs off becoming perfect minions.
The "Iron Star"
Mind Matter and its minions came across a perfect planet suitable for intelligent life. They settled down on this planet. Eventually these exiled Fairies evolved into something completely anew - "Demons". This new race was heavily corrupted, power hungry, greedy, and completely loyal to Dark Matter. They built the most technologically society in the galaxy, and thus their new home became known as the "Iron Star". Mind Matter's plan was complete.
The Second Defeat of Zero
Being seperated from its master, Mind Matter had no idea of Zero's two assaults on the Pop Star and one assault on the Ripple Star. But about six hundred years after Mind Matter's attack on the Ripple Star and the "destruction" of the Humans, Demonic astronauts hauled in a huge, white corpse. There was no doubt about it, it was Zero, but in some other incarnation. Zero Two, as he was known prior to his second defeat, was placed at the center of the Iron Star and hooked up to machinery that would draw energy and darkness form the planet. Zero eventually regained life, and slowly transformed into a being known as "Iron Soul".
The Demonic Onslaught
With its master now restored, Mind Matter decided he would prove itself by conquering the entire galaxy with his completed project. The Demons poured forth and first attacked the Ripple Star, and easily siezed it. They destroyed the Crystal and scattered its pieces along the planets they took control of. They then attacked the Smoke Star, Wood Star, Sand Star (failed), Shiver Star, and the Pop Star. And thus Kirby: Onslaught began.
Mind Matter was finally defeated by Kirby and his allies on the Ripple Star. Its minions were soon killed off in the destruction of the Iron Star.
Mind Matter looks like a pitch black shadow of a very huge Human male. However, it has no gender. There are four red squinty eyes on its "face", as well as two large red eyes on two appendages coming out of its back. Around its hands and feet are white wrappings.
As a manifestation of Dark Matter, it can of course possess unsuspecting (or suspecting) victims. However, Mind Matter's possession is alot more subtle, without any change in behavior until Mind Matter believes the time is right. It also possesses control over the minds of people around it. It can cause euphoria or depression to bravery or panic at will.