This challenge is part of the Meowscles Mischief Challenges, the third agent Fortnite Chapter 2 Season 2 focuses on. You'll have to block damage with a Decoy Grenade.
The difficulty of the challenge lies in finding the item in question and using it at the right time. Once in possession of your decoy grenade, throw it close to an enemy. To compelte the challenge, your decoy must be shot at in your place.
We advise you to launch your decoy grenade in a confined environment such as a house for example. When your clones appear, they will produce a cloud of smoke that will destabilise your enemies, who will be more likely to be fooled and misdirect them.
