Image imported from derpibooru 
Original Description:
 
Sludge in Rage Mode
 
You’ve already seen a picture of this in the fanfic cover for “Go North, Young Dragon” (>>3022157), but it was all darkened with shading and had the colors messed around with so you couldn’t figure out that this was Sludge. Even with these darker less-saturated colors, you probably would have figured out right away who it was.
 
Yes, that mysterious dragon is Sludge and he’s been taking enough things over the years till he finally starts entering “rage mode” like Spike did in “Secret of my Excess”. I have yet to post the next chapter, but it will focus on getting Sludge out of rage mode and essentially getting him reformed. You’ll see how next weekend.