3. Just Loads Of Demons (Action Comics #761)
In a story that is downright mad, Superman and Wonder Woman get transported to Valhalla by Thor (not the Marvel version obviously) to help them in a thousand years war battling the demons of the Vrgtsmyth army. And they do, for ONE THOUSAND YEARS. Sure, at the end of issue they return to the present day, but they have still spent an entire millennium fighting demons. Superman pledged not to kill a single demon during the battles, as they were sentient thinking creatures. Wonder Woman had no such qualms. She slaughters them left right and centre, which leads readers to wonder just how many living things she killed in the span of that thousand years? Millions? Billions? Then, when the battle is finally over, she casually returns to Earth with a millennium's-worth of blood-drenched memories to keep her warm in the winter evenings.