Janemba with all the power he displayed in his various forms, congested into his final form with the sword vs Amazo with all the power he displayed on the show.
DBZ universe is a joke. Amazo takes this no problem. He can't be hurt by energy or anything that we've seen. Aamazo turns Janemba into a flower then vaporizes him. The only thing shown to bother JLU Amazo was solomon grundy and that was PIS with no explanation ever given, and other beings with much more mystical power not being able to duplicate it.
Because every villain in DBZ universe stand there and lets the Hero charge up an attack for 6 panels then lets himself die. They don't try to dodge the big blast only small ones. And then every time they die they come back instantly and stronger. It's like every bad guy there has the same ability as Doomsday to come back stronger than before. Then Goku becomes even more powerful, charges up another blast for about 20 minutes and kills them. Either way energy blast and physical attacks don't hurt amazo. The entire Green Lantern core got owned, then everyone in the JLU. Amazo learned everything in the universe.