I think that the garf-gun attack (as lumpytouch calls it) is definetely the most difficult attack, and the fact that it is so late in the fight makes it impossible to practice. The garfield and jon attack is pretty easy though.
it can be that i just need to find the "sweet spot" so i can dodge the letters. Also have you beaten Monday mode? i'm just asking bc i haven't.
i think the garfield mouth attack can also be pretty hard because in my opinion its really rng based.