Super normal ducks! Bafflehead is based on a bufflehead duck, while Mergandred is a skeletal, oil-covered merganser. Evolution is triggered by leveling up Bafflehead while it holds the Oil Puck item.
They're another extremely specific inspiration. Some seabird surveyors use bufflehead ducks as indicators for pollutant spills, because its easy to see when their white feathers are stained. Thus, a cute widdle bufflehead that becomes a nasty pollution ghost seemed like a great idea. Especially after coming up with this design for Mergandred, dragging its body along with what used to be wings and using its skeletal legs for manipulation.
by stressedoutoddish