Spite Thanos stomps. The DB fighters are great at energy attacks and this is where Thanos durability is supreme. With tp, MM and so on it's a one sided fight. To have a legit shot at him you should add at least Whis, Beerus, Goku and Vegeta.
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Majin Buu would be dropping bombs on Thanos. Thanos does indeed have legendary energy resistance, so he'd hold up fine for a while but...I don't know how he's supposed to put Buu down. So Buu probably wears him down sooner or later.
He'd need to use the gun he used on Thor or something
For BFR victory, yeah sure thing he could our him into a star maybe.
Shields only last for so long, I assume you mean matter manipulation with MM, and I can't recall the strongest opponent Thanks has put down with MM. TP is hard to say, Buu doesn't really have your standard anatomy, does he have a mind to TP **** with?
He could dominate Buu physically if he close the range and gets his hands on him. His shields could take Galactus blast, that depleted much of Big G power before they broke. Buu is an idiot like most DB chars (Goku for example), so their minds shouldn't be that strong. Also, I think that Thanos blasts would hurt Buu more than vice versa.
Those are a different set of shields he has , he needs to prep to have them, his standard personal shields are potent also but break under extended pressure from Champion or one shot from Odin.
But he's not your typical organic being like Goku. And mental strength does not equal book smarts. Goku might be an irresponsible idiot but I bet you he'd make a hell of a green lantern from purely a willpower perspective.
Yes, thanks blasting Buu would leave holes in Buu's body. Whereas Thanos would be tanking Buu for a while, but Buu regenerates and gets stronger with time, Thanos eventually wears. And Buu by no means has weak attack strength, he's far superior to say Assj Vegetas final flash with even lesser attacks given his power level.
Buu does a lot of playing around when he fights though. A lot of non serious behavior because of how strong he is. If he full on blitzed Thanos, yes he'll be on him before Thanks can react.