Asclepius

I did do some theorycrafting when I noticed slakoth on the encounter list. You can only fix slaking in double battles, which happen every so often, using a weezing with the neutralizing gas ability, which you get in the Abandoned Sewers. If you don't mind wasting a turn, you can also use Entrainment to copy a double's partner's ability onto Slaking, I think, which is learned by Chingling and I think Lopunny. But in singles, there's no shot, and you shouldn't bother. And of course this doesn't work if it's a team up with an NPC.