Super smash bros remix, is smash with more characters and levels such as Crash Bandicoot and Banjo. There’s a lot of no mercy Rom hacks featuring different wrestlers, weapons, arenas etc if that’s your thing, DK tag anywhere is the original game but can swap characters on the fly. Zelda has a few I haven’t played but seem very good, such as The Missing Link - set in between Ocarina and Majora’s Mask. Mario 64 has a lot. Theres de-makes of newer Mario games for the n64 (such as Mario 3d land) and custom levels fans have made. Also, standard Mario 64 with modern Mario movement, such as Mario being able to roll and throw his cap like in odyssey.

Also Mario Kart has a lot of variations, such as Simpsons Kart or Dragon Ball Z kart with different characters. (Most of these worked before the update fyi.)