Sure, here's a quick seed. Start on a 32×32 tile map. In the top left corner, drop a row of four tiles that are normally solid but with a hidden pattern encoded in their palette indices: 3‑1‑4‑2. Only a jump that lands on the second tile of that row will trigger the secret. When you hit it, a hidden counter increments, and after the third trigger a hidden flag flips, turning the whole map to black, but the sprite still flickers at 60fps. The trick? The flag is stored in an unused high byte of the CPU's status register, so a standard joystick controller will never detect it. Keep your eyes on the palette table, and the puzzle will stay under the radar.