The Black Jack Taco was a limited edition, Halloween-themed taco, that consisted of a black taco shell filled with beef, Baja Sauce, lettuce and the three cheese blend. It premiered in 2009 and has not made a return since.
Controversy
A news-making scandal with the taco was that it turned the consumer's stool green, as with Burger King's Halloween Whopper in 2015. The black dye is thought to be responsible for the color change.
A Google search, c.2009, of the "green poop" issue.