>>30631929Natures are the easy part with Synchronize, IVs are harder. I recommend catching something with the correct Speed stat to check without even catching them. Just reset if you outspeed them (or if they outspeed you for Trick Room/Gyro Ball Speed).
For example earlier I did Tapu Bulu with a random wild lv 54 Fearow I caught since it has a similar Speed stat with a Neutral nature to Tapu Bulu's +Speed nature when it has a 31 IV in Speed.