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To be honest, warriors in U18 are very humiliated. Dispropotion of strength was huge. Here fight was equal on the beginning. Perhaps, Krillin saw everything. That,s why Kienzan has been done so quickly after first Nappa's ki blast.

I feel like Kwii won't get in the way of them killing Nappa. Or perhaps, just like Vegeta, he'll kill him to start the fight.

Either way, the guys have the element of surprise. If Yamcha tells them about the scouter (or do they know already?), they can go 5vs1 full power and use the Kioken when he least expects it.

Krillin will kill Nappa easily
Haarp & Mr.Popo will beat Kiwi (I thing, that he will escape and explain everything to Cooler)
Ten shin will kill Vegeta after though fight
Yamsha will be heavy injured