My dog chewed up the analog and C-stick.
There are two options here I would consider.
1). If the only thing messed up are the rubber/plastic caps on the sticks (the stick boxes themselves are still good as are the buttons/triggers) then you can just buy
replacement caps online and replace them. To do that you just open up the controller, remove the motherboard from the front shell (pay attention to how everything connects so you can put it back together, it's fairly simple though), then remove and replace the chewed up caps.
2. Let's say you don't want to do that because either the stick boxes are broken or you don't want to have to take apart and reassemble the whole controller. Then you'll first want to buy a
new smash controller (
either color is fine). Unscrew the backs of both your new controller and your old chewed up one, then lift up the backs and swap them. This way you get a brand new motherboard, stick, and buttons but with trigger springs that aren't almost twice as long as they should be.
Method one would be cheaper provided your stick boxes are good, but method two is slightly simpler and maybe you want a two tone controller or new buttons anyway.
To unscrew the back and open up the controller you will need a
tri-wing screwdriver.
Edited with links to Amazon. The only product I haven't purchased at least one of myself are the replacement caps and frankly I'm not sure if they are of good quality or not. If you have other old controllers where the caps are still fine then you can use the caps from one of them.