Emulation itself has been upheld as legal in landmark cases like Sony v. Connectix and Sony v. Bleem . The Slippi netplay mod is also legal, as it contains no Nintendo code and falls under fair use protections for modding copyrighted content.
: Software like Slippi, UnclePunch, and 20XX Training Pack are built specifically to hook into the 1.02 engine. How to Obtain a Legal ISO --- Super Smash Bros Melee Ntsc 1.02 Iso Download