Black hole
A black hole is a dangerous spacial entity found in the Mario franchise. Black holes are, in a way, the equivalent of bottomless pits found in most other Mario series platformers. In real life, a black hole is what remains of a large, massive star if it collapses upon itself following a supernova explosion; its force of gravity at the event horizon is so strong that not even light can escape it. They are not colored black; because light cannot escape from it, they remain invisible in the visible light spectrum.
Black holes first appear in the Mario Party 6 minigame Black Hole Boogie. Here, the duelers rapidly press 
to escape. In the minigame Seer Terror, one of the fortunes is that Bowser will be sucked into a black hole.
Black holes play a much larger role in Super Mario Galaxy and Super Mario Galaxy 2, where they act as obstacles which can suck the player in if they are within its event horizon. The player can only be sucked into a black hole if they fall off some ledges or miss the desired target when using a Sling Pod or cannon. If the player is sucked into a black hole, their Health Meter is instantly depleted and they lose a Life.
The player can also use black holes to their advantage. For instance, any enemies or objects that fall into a black hole are destroyed after falling a certain distance toward it, and in various areas this can be exploited in order to destroy certain enemies. Note that any enemies destroyed by falling into black holes do not yield any items whatsoever. Likewise, any items that do get released by enemies that are destroyed while over a black hole are quickly enveloped by the black hole as well. In some cases, black holes transform into a Power Star after a certain task has been completed. The player is then pulled to the Power Star by gravity in the same way.
At the end of Super Mario Galaxy, after Mario has defeated Bowser for the final time, one of the planets near Bowser's gigantic sun collapses into a massive black hole[1], which will quickly begin to engulf Mario, Princess Peach, Bowser's entire fleet of Airships, Princess Peach's Castle, and even the Comet Observatory. Just as everything is about to be destroyed, Luma suddenly appears in front of Mario, waves at him and then sacrifices himself by throwing himself into the black hole. Thousands of other Lumas soon join him in flinging themselves into the massive black hole in hopes of stabilizing it and ultimately saving the universe from destruction. Eventually, the black hole twists wildly around in space before finally exploding, thereby reforming the entire cosmos and creating an entirely new galaxy, which Mario welcomes in the final cutscene of the game.
In Super Mario Galaxy 2, Bowser is sucked into a black hole after Mario defeats him for the first time in the final battle. He's then sucked into a slightly larger black hole after Mario defeats him for the second time during the same battle; this black hole sucks up the background as well. Princess Peach and the final Grand Star are shot out of the remains of this black hole several seconds later.
Another black hole appears in Mario Party 9, in the background of the final boss minigame, Bowser's Block Battle. It seems to suck in large planets, as well as Mini Stars. When Bowser is defeated, he stumbles into the black hole, although in the final cutscene, it is shown that Bowser and Bowser Jr. can fly normally inside the black hole with their Koopa Clown Cars.
