The Wood Nymph Game Over is an ending which occurs when you accept Tilia's second attempt of infusing you with nature energy/growing your boobies when you have lost to the slime princess or have extracted the Slime Princess' Core before talking to Tilia a second time.
Tilia starts playing and licking your new bigger breasts, wishing she had given them to you. You complain that they are sensitive, but Tilia just wants to play with them more. She ends up finding out that you are a guy because you unload because of how sensitive your breasts are. Her pact with the Director makes it so she has to take care of any men that sneak into camp. Instead she decides to "fix" you, by turning you into a wood nymph. You end up losing your intelligence but gaining a "nice" body. Because of your new body but diminished intelligence you end up making "friends" with almost all of the camp.