First get out a bomb.
Throw upwards as hard as you can.
Don't move, and grapple someone.
then hit them upwards, they should hit the falling bomb one thet fly upwards.
This deals 11% instead of just 5%.
I did this in practice mode....
I did the same thing with Peach and a turnip
I did the same thing with Young Link and a bomb.
I did the same thing as Bowser.