If you want to be 100% legal, do not download a pre-packaged ROM. Instead, seek out the standalone PC version from the creator’s official channels (many of which have been archived on Internet Archive as a historical artifact).
Additionally, the game includes that vary depending on which character you choose. A character with a projectile attack might break blocks that Mario could not, opening up new routes. The game also supports saving , checkpoints , and continue options , making it more accessible than the original NES title. super mario bros crossover nes rom download