I was looking for a Grimer in the trainer school. They have high catch rare, more than 20% when full HP, but I couldn't catch one. I have lowered the HP to red and kept throwing Pokeballs until it KOed all of my Pokemon. Did I miss something? It's not legendary or anything. Why so hard? (this is in Ultra Moon)
Well, @ 20% Hp
> You have a 72.061% chance of capturing it per ball. Thus, you have at least a 50% chance of catching it within 1 ball and at least a 95% chance of catching it within 3 balls.
So, you probably had bad luck :(
Grimer is easy to catch in every pokeball but a beast ball, so use a great ball (97%) or Ultra ball (100%) if you realy still find this hard to catch.