>>39547051First of all I want to say that the distinction between "Mythicals" and "Legendaries" is fucking retarded and only came about because Gamefreak realized they were releasing too many Legendaries and they weren't special anymore. So I'm going to use the terms interchangeably
I like all the Gen 1 and 2 Legends so for those it comes down to taste, but if I had to choose I'd say Lugia is the worst, for a specific reason. Lugia was not in the original concept for Gen 2, and was only added because of the movie being in preproduction. Because of this Lugia is the first movie tie-in Legendary, and set the stage for the trainwreck legendaries would become later. Lugia is fine on it's own but represents a net negative to the series. Special shoutout to Celebi though for being the first aborted in-game event.
For Gen 3 it's probably Jirachi, who basically only exists to sell a bonus disc. Gen 3 is where Legendaries kind of go off the rails and become central plot characters, but it has the benefit of them being fairly well developed over the years.
Gen 4 is a clusterfuck. Lake Trio, Heatran, and Phione/Manaphy (who you forgot on your image but I don't blame you) could all go into the trash and nobody would miss them. Heatran could have just been a regular 1-stage Pokemon.
Gen 5 is Keldeo. As much as I hate the Genies they're at least decently realized concepts, but Keldeo is just shit.
Diancie should be a regular Pokemon. And Volcanion may be bad but Hoopa looks like a Yokai Watch character. At least people remember Volcanion exists; when is the last time you thought about Hoopa?
Finally, the Tapus are completely unfun but as a concept they're okay. Marshadow is a loreless piece of this though, and Zeraora is the single worst Legendary of all time.