Mandalorian S2.5 (Also known as Boba Fett).
Disney attempts to turn a cold blooded bounty hunter into a nice guy and fails miserably. Maybe it was a bad idea to start with?. The Tusken Raider back story was moderately interesting, but other than that nothing was interesting until the Mandalorian returned.
The worst episodes in general, were the ones directed by Robert Rodriguez. Too many tropes, 'homages', etc. Ray Harryhausen style stop-motion in the first 2 episodes, really bad practical effects (which I know they desperately tried to salvage in post, but there's only so much you can do with crap footage) and then the stupid King Kong re-enactment in the last episode.
...but...most of all, it failed because it tried to turn Boba Fett into a nice guy.