Kid Buu upon defeting Goku and the rest of the z fighters he continues as he wanted.. destroying his universe upon which he gets very bored and as a result very angry and so rips a dementional barrier to the DCU, where after destroying a few planets he comes to Apocalypse to which Darkseid doesn't Like so they start fighting to which Buu absorbs him and now Buu has become so much stronger than before. Now with darksieds mind he has become smarter like when he absorbed piccolo. He is wanting a challege and with darkseid mind he knows of a very powerful person. He heads to earth looking for the Man Of Steel but on his way he wants to have some fun and starts blowing up every planet. He gets to earth but he ends up in gotham and is confronted by the Bat. Batman not knowing what this thing is does what he does best a batarang to the head but it doesn't work. Buu was wanting to destroy him but he was getting a feeling that he should just absorb him cause his mind would come in handy. So with buu now absorb with Darkseid and Batman he heads out for the man of steel.
Once Superman knows whats going on he decides to go take him out but the rest of the league goes with him. Even Villians are joining in the fight to try and stop him can they do it?
Kid Buu keeps his own personality but has the brains to go along with it now.
so Kid Buu has all his own powers and darkseids powers and his brains and he has the brains of BATMAN now that could be prove to be dangerous.
Kid Buu
Vs
DCU
This is not about popularity who would truly win.