In episode 2, when Oubu ascends to the surface, an old man describes it as "a part" of the thing that razed Ueno.
In what sense is Oubu "a part"? Oubu at this time does look slightly different than it did during the incident in Ueno (probably just because Oubu changes shape a bit depending on how powered-up/powered-down it is). Now:
But Oubu (unlike Entei) was no more or less "complete" now than in the past, so I'm not sure what the old man means. (Maybe he's just senile?)