Ultraman is pretty creepy sociopath, but his rampage at the Daily Planet really shows off his creepiness. One can only imagine what he was going to do to Lois Lane before he was interrupted.
Ultraman: Superman isn't coming. No one is.
The descriptions of how ARGUS personnel was decimated after the Crime Syndicate arrived are actually quite gruesome.
The Hyena reportedly eats his victims.
What Professor Pyg did to the musician in Issue 1 of Arkham War.
A gangster named Eel O'Brian gets doused in barrel full of chemicals when Owlman ambushes his gang. He ends up slowly melting into a puddle while still alive. However, It doesn't show whether or not he died and he may come back with superpowers. Maybe as Plastic Man.
Whatever the Volthoom entity did and most likely does to Power Ring in order to get "charged." The Nothing Is Scarier trope is utilized, but judging from what happened to the Earth-3 Abin Sur, it's pretty clear the ring is slowly killing Power Ring.
Worst of all, its been let loose with Power Ring's death (which he was grateful for after dealing with the ring) so some other poor bastard is going to get it.