It is unlocked by beating world 8, but it will automatically be unlocked early on Wii Us with New Super Luigi U saves on them. In it you can play as two different versions of Luigi simultaneously.

BOTW Save Manager for Switch and Wii U. Contribute to DeltaJordan/BotW-Save-Manager development by creating an account on GitHub.

World's Smallest Nintendo Wii, using a trimmed motherboard and custom stacked PCBs - loopj/short-stack ...