This challenge is part of the Fortnite Midas' Revenge series of challenges. You'll have to consume legendary loot when you're a Shadow. Since update 14.40, you become a Shadow after your death — in normal mode only.
One of the skills of your new kit is the absorption of items (ammo, materials, weapons etc) that will allow you to regain small amounts of HP as a Shadow. This challenge will require you to consume items of legendary quality.
It's not complicated at all, but you'll sometimes have trouble finding legendary items. Players are often willing to kill to get their hands on them when they see them!
Below are a few places where players are likely to leave legendary loot.
Map
Doom's Domain and Stark Industries are the best landmarks to find these items in Season 4. They are guarded by a NPC who gives a card to open a vault where legendary weapons are sometimes numerous.
By turning into Shadow early in the game, try to stay close to these vaults. Attack and kill the living who venture into them and consume their legendary items. Even if there are no players lurking around, always check the vault to see if a legendary weapon or superhero power is lying around!
Original content by Romain "Zorg" Becquelin.
