I've seen all these cool new features that we are getting and they're all really really nice. However the one feature that I've always taken for granted on showdown is the cancel button after clicking a move or clicking a Pokemon to switch into. I can't remember how many times I've been in a battle and I think,"If only I clicked this move instead". I'm sure many people have also miss-clicked a move and had to deal with the consequences of that mistake.
I believe that the cancel button would be a really great addition to our battle UI. It will make the game a bit more well rounded and fun in my opinion.
If this is a feature that has been thought about in the past (I'm sure it has) then please add it to the game whenever it is possible. Thank you! :D