Over the years, Magic: The Gathering has had a lot of odd mechanics that nearly made it. Gunk is one of them.
Magic: The Gathering almost had a mechanic where you were allowed to bring in very old cards to play in newer matches. And everything was nearly broken.
In the late 2000s, Magic nearly had a new mechanic (ominously) called "Forbidden." It almost made it.
One mechanic in Magic history was so broken that Wizards of the Coast named an entire scale of game mechanics after it.