This is a missable achievement, so make sure to save BEFORE you enter the area that starts the run!
The goal is to carry Rottytops all the way back home without taking any damage and in a single run. If you take damage, you'll have to reload your save file or it won't count.
Near the end, there is another save spot; if you've made it that far successfully then you are safe to save and still be able to get the achievement! If not, DO NOT SAVE, reload your save and try again.
Right after that save spot is a Cacklebat that you have to jump over and then it's a safe run the rest of the way.
I made a full image guide on Steam, and I'd have posted it here but I can't figure out how to include images, so here's a link to the guide I made:
https://steamcommunity.com/sharedfiles/filedetails/?id=22797...