The Crystal

The Crystal is a direct power source for Matt, Chianti, and Beau. It also is a source of magic for everything on Earth.

Powers
The crystal is a psychic source of power for the Basement Trio, due to them being the inherited guardians of it. Due to their connection, if it is shattered, the three of them will die.

It also has provided Estelle with a surge of visions.

Background
The crystal had previous Guardians pre-basement trio, numbering to about five of them. These were all relatives to Matt, Chianti and Beau, all parental figures of some sort. At an unnamed point in time, they had all vanished protecting it. Due to this, they were all presumed dead, when in reality they had been transported to another realm by it.

They had passed on their title of guardian to their younger family members (though Beau is not a daughter, she is a niece of one of the protectors.)

Trivia

 * The fact that it had come from another realm implies there are more than one.
 * Do not touch the crystal. It's ability to give surges of power has nicknamed it "Crystal Magic Meth"