How would you breed for it?
1. Put male Croagunk and female HA Croagunk in the Day-Care.
2. Walk for a while, reject the first Egg (*shrugs*), save.
3. Walk a bit more, get the second Egg.
4. Hatch it, check if it has Poison Touch (Hidden Ability).
5. If it doesn't, reset and return to 2.
6. If it does, reset, take both Croagunk and put two Skrelp in their place.
In theory, it *shouldn't* work because the mother doesn't have Adaptability, but we don't fully know how breeding works this gen so it's possible the HA flag is set for the Egg along with the inherintance spread and such. This is why I think it's worth a test.