One feature missing from Switch Online's Nintendo 64 library is Controller Pak support. Back in the day, it functioned as a memory card and could be used to store and transfer save files and other data (like Time Trial Ghosts in Mario Kart 64).
While it can't be used in the Switch's N64 emulator, datamines have revealed how Controller Pack support has been present for some time now. And while it's not been officially activated (at least for now) community hacker LuigiBlood recently shared a how-to, which resulted in the following demonstration:
Unfortunately, this is not possible on a retail Nintendo Switch (in other words, you'll need a hacked one), and even then, there's some trouble. When games are reset the ghost data seems to disappear - although the save state version will keep it.
Nintendo's most recent update to the N64 library added Rare's classic 3D platformer Banjo-Kazooie and fixed some emulation issues in The Legend of Zelda: Ocarina of Time. With any luck, one day we might see Controller Pak support officially added to Switch Online's N64 library.
Would you like to see Controller Pak support added to Switch Online at some point? Comment down below.