Both part 3 and part 4 have a major tonal shift as caused by character death, Stardust Crusaders is broken up into two smaller parts, one where they travel to Egypt, and then the part where they're in Dio's mansion, and Diamond is Unbreakable is broken up into two parts, where they meet local, mostly harmless stand users, and where the genre shifts to more murder mystery.

The two parts are distinctly cartoony and dark respectively, but the opening always changes from the lighter opening to the dark one like, 6 episodes early.

WTF.

Oh, I almost forgot.

They also had a somber, reflective ending theme for the last half of Stardust Crusaders, but didn't play it when it would have had the most emotional torque. What the fuck, guys.