In Super Mario Bros. Z, Mario stomped Captain Basilisx's best friend into a lava pit, but Mario doesn't remember it. Although Fridge Brilliance sets in when you realize that there are no lava pits in the room that Basilisx mentions. Mario may not remember it because it may have never happened in the first place.
In Death Battle, this is the stated reason why Guts manages to defeat Nightmare in their battle. Guts has always fought impossible odds against terrifying demonic forces due to the brand on his neck attracting them like moths to a flame, and yet Guts has also always managed to come out on top if only through sheer dumb luck and unstoppable willpower; Nightmare and the Soul Edge really aren't anything he isn't already accustomed to.