suppermariobroth:

The Nintendo Switch Online NES version of Super Mario Bros. 3 contains a visual glitch in the first fortress of World 3. If Mario runs while passing between the second and third door inside the fortress, the background will briefly shift and blur in a manner not possible on original NES hardware.
_{Main Blog | Twitter | Patreon | Store | Source: myself,Super Mario Bros. 3(Switch Online),original hardware}