Last month, at GDC 2018, prototype footage of the Nintendo games ARMS and Splatoon was revealed.
The prototype footage of ARMS takes a look at the control scheme, the hit meter, 2v2 gameplay, and minigames (including a bowling prototype that did not make it into the final game). The development team stressed that visuals are not important for prototyping.
When it came to Splatoon, the development team had over 70 different design proposals and a number of software prototypes. The initial prototype featured a cube-shaped character (called “blocks of tofu”) that players moved around a flat map that shoots white or black ink.