That crane boss in FF7 that can grab up to two of your party members, kill the third, and make the game believe that’s a totally defeated party resulting in a game over.
The last boss in Super Widget for the SNES.
Dark World Dungeons 1 and 5 in Zelda 3.
Special World Stage 2 (the P balloon level) in Super Mario World.
Every world in Super Mario Bros. 3 is legitimately harder than the last, adding a feeling of escalating difficulty to what is otherwise an easy game.
The vehicle segments in Gears of War 1 and 2.
Wily Stage 2 in Megaman 10.
Finding the needle in Jupiter in the seventh Dr. B game.