There are spoilers for the story mode of Super Smash Bros. Ultimate here, mainly regarding one of the challenges in World of Light and the final boss. You've been warned! Just in case, all spoiler-related text has been hidden in a spoiler block quote.
I've reached a point in World of Light where I've beaten all the spirit battles (at least, I think I have) except for the final boss.
How can I guarantee that I will beat both Galeem and Dharkon and receive the Duck Hunt challenge ("Beat the final boss without being KOed"), though? And does this imply that you need to lose absolutely no stocks in all 3 phases, or just the final phase (I've heard that you get your stocks revived after beating the first 2 phases)?
Continuing on with this, (Spoiler below)
What happens if I don't meet the requirements for the challenge but still beat the boss? Will I have to restart WoL all over again just for this one singular challenge? Or, is there some kind of method that will 100% guarantee the completion of this challenge?