I saw the original cover for Green Lantern Corps #20 on Newsarama and really thought nothing of it. I tend to skim through those and only occasionally get really excited about something 3 months down the road. But then I went to The Straight Poop, which is GLC artist Patrick Gleason's blog, and he posted the hi-res, and much larger, version of the cover.
Seeing Mongul with a yellow ring on is terrifying. If you don't remember who Mongul is, how about a little refresher course, courtesy of Wikipedia:
Mongul possesses extraordinary superhuman physical attributes. He demonstrated that he actually was stronger than Silver Age Superman himself. In addition, he was invulnerable to nearly all forms of physical harm. Superman at one time did defeat Mongul, by going all out with speed and strength and heat vision, but fell into unconsciousness immediately afterwards. Mongul also seemingly had the capacity to create dimensional-inversion cubes, designed to prevent escape by warping their interior reality and absorbing any power used against them from within. Whether this was an actual power or merely a sophisticated technological device remains unclear but it general believed to be technological device. He also seemed to possess a limited capacity for telepathy, and the ability to teleport himself across even interplanetary distances.
If you read the entire Wiki entry you'll also find out (like I did) that the Mongul that is currently ruling Warworld is actually the son of the Pre-Crisis Mongul that I knew of growing up. And while the original Mongul was toned down in terms of power, supposedly his son has all of the power he had before, which is what is listed above. Typical Dc to muddy up good characters with a bunch of bullshit tampering, but whatever, give him all that power plus a yellow ring and he is simply terrifying.
The best part of his backstory though is this:
In the meantime, he sought his sister, Mongal, to settle family squabbles. The heroes broke free and used a teleporter to transport Mongul and Mongal to their home planet. Stating family to be a weakness, Mongul punched off Mongal's head.