A/N: this has to be the most difficult question I've come up with yet. How strong is this incarnation of Buu from Super Dragon Ball Heroes.

This is Xeno Buu powered by the 3 Star Dark Dragon Ball (not Black Star Dragon Ball), which gave him an enormous boost of power.

He soon absorbed Demon God Dabura.

Demon God Dabura was shown to be stronger than Xeno Buu. So Xeno Buu absorbed him and boosted his power further.

Then later on he absorbs Xeno Janemba who was powered by the 5 Star Dark Dragon.

To become to form he is now.
You 

(Which technically means he has two dark dragon balls now as well as the powers of a Demon God).

Austin: this is one of the largest power boosts I've seen so far in Super Dragon Ball Heroes.