The core appeal of the game is the roster. You aren’t just playing a palette swap of Mario; these characters play exactly like they did in their original games, but adapted to Mario’s physics engine:
This is a gray area. Here is the breakdown: super mario bros crossover nes rom download
Because the game uses unauthorized intellectual property, Nintendo and Capcom have issued DMCA takedowns in the past. The original Newgrounds version was removed for a period. Therefore, no one is legally selling or hosting the game with permission. The core appeal of the game is the roster
That said, no major company has sued individual players for downloading the offline version. Enthusiasts generally consider it an abandonware fan tribute, but legally speaking, downloading the full game from a random ROM site is still copyright infringement because it contains unlicensed assets. but legally speaking
Safe recommendation: 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 Instead, seek out the standalone PC version from the creator’s official channels (many of which have been archived on Internet Archive as a historical artifact).
Developed by Exploding Rabbit, Super Mario Bros. Crossover is a fan-made Flash game (later ported to HTML5 and other formats) that takes the classic 1985 Super Mario Bros. gameplay and flips it on its head. It is essentially the original NES game, reprogrammed to allow you to play as characters from other iconic NES titles.
It is the ultimate love letter to the 8-bit era.