Have Ness use his PK Flash (You know, the green lightning thingy used by his Regular B button?) on Mr. Game-and-watch while Mr. Game and watch uses his bucket (Down + B). Repeat this until his bucket is full. Afterwards, use the loaded bucket on your opponent (Or Ness if he's your opponent/friendly fire is turned off.) and it should do around 300% to 400% damage, creating an Instant KO! Sure to work!