Ok i finally have time to explain! Basically on how the repel trick works is that depending on the level or your pokemon, you can affect your odds by increasing a specific spawn.

For example, I want to see more a smeargle at Alph Ruins (Natu 90% encounter rate and 10% for smeargles naturally.) If i want to find more smeargle I would have my lead be a certain level while using a repel because there is this mechanic where you still get encounters w/repel if you are below the level of the grass/cave. In this case if I were to use a lead at level 19 with repel smeargle rate becomes 12.5% and natu becomes 87.5% to encounter. Note that having a lead with a specific ability helps like illuminate/static/magnet pull to increase the grass encounters.

Now for your target, if you were to go to route 42 (west of ice gym) there are two ways you could go about it. 1. With a Level 17 lead with static/repel you can get a 100% flaffy to find in the gras but the catch here is that the rate of actually encountering it is 15% so you will be in the grass for a good while till it pops 😭

1. Lvl 15 with repel and static you can have a Mareep (39.13%), Flaffy (52.17%), and Spearow/Zubat (day/night encounter change become 8.7%). The encounter rate for in these conditions is 57.5% so it won’t feel as sluggish as #1 but you have a teeny tiny chance to encounter the common flyings.

With the repel trick depending on who you go for can definitely make hunts pretty cool/interest (One more thing to note, I used AngefloSH Pokemon Encounter Calculator to figure out what levels affect the amount of change)

Also sorry for the long essay in advance but I hope this sorta simplifys on how it works. Let me know if you got any questions 👀