Let's assume there was a prize for stupidity in phenomenal measure - which 2hu would win it?
Birdbrain probably would have the least chances because her stupidity largely is built on fan cannon. Rotbrain on the other hand has a proverbially decomposed brain and can't do much other than reciting poetry when not under the control of her mistress, making her passively stupid. (9) finally is widely considered to be the ⑨ Champion and has her stupidity as one of her primary defining character traits, especially when attacking those much stronger than her, making her actively stupid.
Any suggestions?