Hello, so I don't really plan to speedrun this, but I see everyone talking about banning up+down. The only version I played is on Switch Membership (And because Switch has directinal buttons not as dpad I can press up+down). It doesn't do anything? The second press just cancels the first? I guess it might just be patched on Switch, but I still would like to know what up+down actually do and why is it bad for it be a thing?

In general, Games on the SNES aren't programmed to handle Up+Down at the same time as the D-Pad on the Controller prevents it from happening (without using force).

In A Link to the Past, a lot of the things in-game break from it. Screen-Transitions beeing a main problem (the game assumes you transition in both directions at once and has no clue what to do, so it does something). In TAS this is used also a lot for movement optimisations not possible easily with a controller.

The Main reason it's banned for all RTA Categories is the inability of using it on a Standard Controller without either Modifications or a lot of force (and possibly damaging the controller).