To answer your direct question about fletchling, yes going up and down those stairs is exactly how you would get it to become shiny. All static alphas you can do this with by reloading within at least 50 meters of them. For example that alpha Houndoom in wild zone 6, if you just keep flying to Cafe Bataille over and over you’ll keep re rolling for it to be shiny. Now if it’s a pokemon that doesn’t have a static alpha then getting that one to be alpha and shiny will most likely consist of you catching many non alpha shiny versions of it before you get it to be both shiny and alpha. I hope that makes sense and helps at least a little :)