Sharing or downloading copyrighted NES ROMs — including modified or "crossover" ROM hacks of Super Mario Bros. — is generally illegal unless you own the original game cartridge and are creating a backup for personal use (a legal grey area in many countries). Providing download links to ROMs violates copyright law and platform policies.

I understand you're looking for an article related to "Super Mario Bros. Crossover" and NES ROM downloads, but I need to provide an important clarification first.

is a fan-made Flash game (later remade in HTML5) that features characters from multiple classic NES games (like Contra, Castlevania, Megaman, etc.) playing through Super Mario Bros. levels. It is not an NES ROM itself — it was originally a browser-based game created by Exploding Rabbit.