Muk advice
I try to be different with gym mons than the usual that we always see for diversity especially with mons i like. So i have a muk with 89% IV, CP1518 and moveset infestation/gunk shot, should i power him up to be used as a defender? I know poison jab is probably the better quick move but this is still rated as an A for defending. Also grimers are pretty rare to me with only 19 caught/hatched and this was the first grimer i got over 80+ IV
Answers
Not mentioned yet:
One plus is that infestation, like poison jab, continues to hit grass types for super effective. The downside is that it doesn't get STAB and is resisted by fairy where as poison jab gets DTAB and hits fairy hard.
Another thing is that at least you didn't get dark pulse!
Lastly, if you were to re-roll, I personally would be content with PJ/Sludge Wave