I'm confused about Obito's role in a bunch of stuff. Was Obito responsible for the bloody mist or did he make it bloodier as the defacto Mizukage? And how involved was he in the Uchiha Massacre? I've heard interpretations that he carried out majority of the massacre and Itachi only killed his parents but I'm not sure if this is true or not. And what exactly did he do in Rain? How much was Danzo and how much did Obito screw up? Idk I'm so confused. How much did he fuck up before even turning 20?
For the most part, that depends on whether you’re reading the manga or watching the anime, and also whether you cannot math, apparently like Kishi.
The anime really likes to downplay Itachi’s actions and make him even more of a hero (understandable, I suppose, given how popular he is, but I find it :/ ). Case in point: having Obito carry out the massacre, up to and including killing Izumi. That doesn’t happen in the manga.
With the Bloody Mist thing, Obito can’t have started it - Zabuza participated in the graduation fight when he was an Academy student, and he’s the same age as Kakashi and Obito. Obito wasn’t playing Madara at age 9. So maybe he had a hand in the bloodline purges, but it’s hard to be sure, since there’s nothing about his actions at the time, really. It’s implied that he had a hand in making Kiri into the Bloody Mist, but the timeline means it already had that nickname when Obito was a child, so.
Also, in the anime he’s involved in Danzo’s plans against Akatsuki, while the manga never shows that. (And that whole timeline of Obito trying to turn Yahiko/Konan/Nagato to his side is kind of suspect, given ages and how it’s supposed to have happened during the Third War, most of which Obito spent either in Konoha or trapped in a cave relearning how to move. Like, when did he even have time to approach them? Obito spent several months [as shown by hair growth] with Madara before he saw Rin killed, and the Kannabi Bridge incident pretty much ended the war, so if anyone approached them it must have been either Zetsu or Madara. Also the ages of the Ame trio don’t match up well?? Idk, it’s frustrating.) All of the rest of it - taking over Ame, killing everyone even vaguely connected to Hanzo, etc. - was Nagato years later.