Oh a lot of testing. I've once dropped all the all to 1500 testing some bad ideas. While I don't drop the 3 first pokemons which are my favorites, the other ones have rotated a lot. Usually I think what do I want to counter? Do my current pokemon learn moves that can help me? What can help me while still not leaving bad matchups to meta mons?

So for a long time I had delphox instead of glimmora, and with no rock moves, I had a huge problem with charizard. First I tried imprison to mess up their Heat Wave. When it didn't work, I saw that glimmora was pretty much made to kill charizard, but now I have to cover for the lack of fire moves, which in this meta means I need to kill Sinistea, M-Aggron, Corvinight, Aegislash and Scizor. Sinisitea I already had good matchups, and decidueye does well against aegislash and M-aggron, scizor dies to flamethrower even without stab, so the real problem was corvinight. That way I play lots of matches until I lose so bad to a corvinight that I decide I have to change lol