In light of the imminent shutdown of the 3DS and Wii U’s online services, I’ve been revisiting Kirby Battle Royale and Mario Tennis Open over the last few days - as relatively obscure spinoffs with regional matchmaking on a decade-old system, it’s been nigh impossible to find an online match in them for years, but with the shutdown causing people to revisit these old titles one last time, it’s actually been possible to find matches again, and it’s been pretty darn fun.
The Nintendo Network service, that handled online play for the vast majority of 3DS and Wii U games, Splatoon included, was shut down on the 8th of April. So yes, the official servers for Splatoon are dead.