Hey Guys And Gals, Here is my 100% Achievement Guide & Full Walkthrough for Wailing Heights!
The very first time you take control of Debbie the Zombie, once you leave the main stage area and are in the sort of dancing bit with all the zombies in, go to the left and you see a guy behind a sort of bar? (You know, like the ones they have in cinemas?)
Anyway, hes selling a few items, so go and talk to him and order absolutely everything you can off him (Just exhaust all dialogue to be sure).
But he will have one thing missing so we need to come back later.
A Little bit later on, Once you are in the back of the Ruff House with Abnorm and pass out due to the Moonshine and end up outside Town Hall, NOW we can get Debbie and ask for the last item on the list from the vendor guy. So go back to the Souless Saloon, and ask for the Atomic Toxic Blobtail 236 and achievement should unlock!
Go to 33:10 for the first part of the achievement and 51:55 for the second part!
Hope This Helps!