We now have all the Master Weapon Assernal, but Jack wants you to destroy them? Let's see what he wants us to do.
Jack: It is true that I want to destroy these weapons, but that's how the Master Weapon will be made. Take these weapon to the Dark Tree and destroy them.
Destroy the weapons
Demongo: No! My precious weapons! Gone!
Jack: It is done. Come back here and I'll tell you why this must be.
Talk to Jack
We now learn after collecting more than 20 weapons, it turns out YOU are the Master Weapon. You thought you would've gotten a super powerful weapon, didn't you?