The minimum All-Star score(s)

The answer seems to be that you have to get 5 hits on x number of people streetpassed, rather than number of people. For example, I street passed with one person two days ago and killed him in < 5 hits, but then streetpassed with two people yesterday and killed them both and unlocked the challenge.

The point of hitting the bomb is so the bomb move faster and it does more damage to the structures before exploding. If you just hit the bomb of at about *25% it will only be able to damage the the two types of wood blocks. At around *30% percent you can start to damage the light grey stone blocks and *40% you can damage the dark grey stone blocks.

The higher the percent the better because the bomb will lose speed with every hit to the structural objects. It does not affect the bomb's explosion, just how the bomb moves.

*Rough estimates based on game play over the last few days.