Spoilers below for anyone who doesn't wanna get spoiled by manga. New arc started in the manga, but zero broly spoilers.
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1. I know people are saying the whole "can't resurrect people people killed by demons" thing is just the same stuff we knew from the Piccolo arc, but I still strongly believe they are basically saying the demon realm have their own versions of kaioshin and gods of destruction
2. Friend of Belmont was probably OP as fuck but I guess we don't know if he was stronger than Jiren. Sounds like probably not.
3. Fucking Jaco
4. Regarding needing the guy who Buu ate, I think it is very likely all the supreme kais know how to deal with demon realm magic and the general types of fuckery that the demon realm gods can do. But since Shin is a newby idiot, he probably doesn't even know they exist. So eventually Shin will be like "since when are there demon realm gods?? lmao!!" and then the old kaioshin will hit him on the head and tell him he's an idiot or something.
5. Next arc is probably something along the lines of the demon realm rebelling against the non-demon realm? The supreme leader of the galactic patrol got frozen by a demon? And the fat dudes needs to heal him?
Stoked! Long live dragon ball!!!!!!