World 3 (Super Mario Bros.)
World 3 in the original Super Mario Bros. was crazy. All of a sudden, it was night time! And there was snow everywhere, kinda! And, um, who are these jerks jumping and throwing hammers? When the sun went down and the snow fell, the difficulty ramped up. World 3 was when Super Mario Bros. really stopped messing around, and that combined with its jarring scenery change make this still memorable today.