How can I guarantee that I will beat the Duck Hunt challenge (grants Mew spirit) in World of Light?

There is no real way to guarantee you'll beat the challenge, but there is a way to guarantee you'll unlock it (explained below).

If you want to legitimately beat the challenge, these are the important parts to know about:

• (in case this is not obvious) you can use any character for the challenge. You do not need to use the Duck Hunt Duo at all.
• The challenge is not limited to only the boss fight. It applies for the entirety of the final level. This includes the platforming section at the very beginning. You are absolutely not allowed to die. At all.
• You can get the challenge on any difficulty, including Easy.
• You do not need to restart WoL if you fail the challenge. In fact, you can experience all 3 endings without restarting WoL.

Some tips to make it easier:

• You can attack Galeem and Dharkon during the platforming section. Hit them enough, and they'll leave.
• Equipping spirits of the same franchise gives them a boost in power. The higher the power, the more damage you deal, and the less you receive in return.
• [This was accurate about a year ago and needs to be reconfirmed] If you know how to handle Olimar, for some reason his aerials are both weapon and physical attacks. As a result, you can double your attack bonus via both the skill tree, and your spirits. If done properly, you can defeat Giga Bowser in as few as 3 shots.

If the challenge truly is too hard, you can still unlock it using a hammer.

Simply select the hammer (if you have one), and then select the challenge you want to unlock.

You can earn more hammers by unlocking a certain number of challenges (either legitimately, or using the hammer). Obviously, hammers are limited, so keep them for challenges you cannot beat yourself.