GameCube. Because I have fond memories of it in my childhood. I prefer it over PS2 because it properly supports 4 player games (without any extra gadgets).
Smash Bros. Mario Kart. TimeSplitters. All excellent couch multiplayer games. Even Metroid Prime 2 had quite fun multiplayer.
0.999… means infinitely repeating 9s. There’s no more 9 to add that hasn’t already been added. If you can add another 9, then it’s not infinitely repeating.
JSON for serialization all the way. It’s simple and to the point. It does one thing and does it well. There’s little room for annoying surprises. Any JSON can easily be minified and prettified back and forth. If you want it in binary format you can convert it to BSON.
Yaml is too much of a feature creep. It tries to do way too many things at the same time. There are so many traps to fall into if you’re not cautious enough. The same thing can be written in multitudes of ways.
One way to tell if two numbers are equal is to show there’s no real number between them. Try to formulate a number that’s between 0.999… and 1. You can’t do that.