Retro is a secret level in A Koopa's Revenge II. Beating it leads you to World 4-1.
- There is a secret pathway that leads you to World 5-3, the final level.
To go there, simply jump over the flagpole at the end and enter through the castle door (press the up arrow to do so). There will be another flagpole waiting for you after the other set of stairs.
- This level is based on the first level in Super Mario Bros.
- The enemies act like the enemies in the first level in Super Mario Bros.
- Toadlet - Goomba
- Yoshi - Koopa
- This is one of the only levels without special coins or any of the Baby Bros. Another one is Final Confrontation, which is unlocked after collecting all special coins and Crashed Airship, which is where the beginning of the game takes place.
- Like in Super Mario Bros, the screen can only scroll to the right.