This means that games that heavily rely on online services, like the original Super Mario Maker for Wii U (and 3DS), Mario Kart 8 and Splatoon's online multiplayer, and several other games will effectively stop working, more so for Super Mario Maker since that game is entirely relying on online user-created levels for the gaming experience.
However, all is not lost, as the fan and homebrew community is here to save the day (as is always the case), even in the most dire of events like the closure of all online service for said consoles, with the great community network known as Pretendo.
Pretendo is basically an entirely open source project that aims to replace Nintendo's network for both the 3DS and the Wii U, and even their respective emulators like Citra (or its forks given its recent demise) and Cemu, which will allow all users to interconnect with each other even after the demise of Nintendo's own servers later today, and while their compatibility isn't entirely 100%, they developers behind the Pretendo network are still hard at work developing the service so that more and more games get proper compatibility.
Those interested in trying out the Pretendo network can follow their own installation instructions found at their site, which includes installation guides for both Citra (or its forks) and Cemu, and in the case of the original hardware, the user will require a hacked console, be it a hacked 3DS and/or a hacked Wii U, depending on which console the user has. Just be aware that your current Nintendo ID (and everything that it entices, like friends list and other things) will not be carried over to the Pretendo servers, as Nintendo's servers hold that data, and repurposing the original ID for Pretendo could pose a severe privacy violation, so a new ID will need to be created for usage with Pretendo's servers.
A recommendation for a more detailed look into the Pretendo network is a recently released video by renowned game developer and homebrew enthusiast, Modern Vintage Gamer (MVG), gives takes a deeper dive into it, as well as its current status, usage, game tests and installation of the fanmade network into your own consoles.
Source Pretendo Network
