|Information in this article is non-canon|
This is a term for a Friendly Sharptooth that went bad. Ichy and Dil were Dark Sharpteeth, though they eventually became nice again. Chomper, Andromeda, Thorn, Lorenzo, Dakota, Flavia, Farrell, and Flavia nearly became Dark Sharpteeth.
Dark Sharpteeth are more dangerous than your average mean Sharptooth, as, having been around Leaf Eaters for a while, they know the weaknesses of the Leaf Eaters they have been around, making them deadlier hunters.