The Kubrik's Kubes are a set of kosmik... err, cosmic artifacts, older than the universe. They are powerful, colorful puzzle boxes, but their true purpose is knowledge. If you solve the puzzle, you gain enlightement; if you fail, you descend into madness.
They have shown up on multiple worlds, and uplifted the people of the Tooniverse; the Planet of Amateur Contract Law guarded many, one of which fell into the hands of Psychovant the Duck. In truth, all of the Kubes were facets of the true Kube, an eleven-dimensional hyper-hyper-hyper-hyper-hyper-hyper-hyper-hypercube at the center of the Omnilooniverse, grown around the One True Ending of the Cosmic Plot Device Caper.
When the universe was rebooted during Just Another Multi-Writer Cascade That Will Probably Never Have an Ending, all of the Kubes lost their power, becoming inert hunks of multicolored plastic. However, they retain the ability to channel kosmik energy; Net.Access used one to bring together the unfinished spirits of the planet Rostir, and another was used to resurrect Obscure Trivia Lad, substituting for the shard of the Cosmic Plot Device that had originally powered his android body.
Kid Not Appearing In Any Retcon Hour Story once mentioned the "Cosmic Rubik's Cube"; this may have been a reference to the Kubes, or to some other cosmic artifact that's also a parody of the same plot device and toy.