Thanks for trying the game. Yes the mutation means one of the other traits has been randomly changed, and color has a high likelihood of being the mutated trait. Additionally, Bae has a 50% chance of being a random color or 50% red (something something chaos). I have an update already done that I finished day after grace period that shows a collection of all the eggs you have saved, and also shows what each characters traits are, but I have to wait till after review window to release it.
I agree the stethoscope is OP, and only a mutation on the catchphrase can make it confusing sometimes. I do like the idea of only allowing it after some amount of wrong guesses.
And yes, after you use half of your tool uses/guesses, there is a voice line that happens. If you want more silly dialogue, there is a unique one for every character if you lose with them guessed correctly as well, though they are short.