What does it change between versions 1.2.0 and 1.0.0?
I want to know because i want to get into speedrunning the game, but the cardridge I have is in 1.2.0
1.3 is the fastest version of the game. if you update your copy to 1.3 you'll be running on "1.3 physical" which has slightly worse load times, but unless you're a top level runner it won't really matter
Recent runs