Well my new idea would be a chicken with a secret agent suit, which is very, very rare that it appears in the waves because this chicken will give you a special key that will unlock what you want just by having that key, if that idea is very OP will only give you 5 normal keys.
I would also like to see if anyone has some ideas to add them to my ideas of the challenge mode (link here to the post): Ideas wishes for the new game - #25 by xXmlgDiegoXx