Taken down for pretty gnarly security fixes.
The online services for two Wii U games are actually coming back soon.
A social media post from Nintendo UK announced that online services for the original Splatoon and Mario Kart 8's Wii U version will be restored on 3 August.
The servers were taken offline in March in order to resolve an issue where data could be sent to the Wii U that would cause remote code to be run on the system. The flaw, disclosed on Christmas Eve 2022, affected Switch games (which were all updated) and Mario Kart 7 on the 3DS.
