Kanzenshuu

I don't know if this is a plothole, but it is unexplained:

-When Goku and Vegeta were inside Super Buu's body, their small size made them a lot weaker to the point that Goku's ki blast couldn't cut through Super Buu, yet at the same time Super Buu was powered by a Mystic Gohan and SSJ3 Gotenks of ...

The elder kai gave Goku his remaining life, wouldn't that mean Goku already has a long life?

As long as we're talking about the most powerful move independent to the user (if a person with a power level of 100,000,000 were to have every move used in dbz, which one is the most powerful). I'd say hellzone grenade is the strongest.