One of the new skins in Fortnite added at the start of Season 4 gives players an ability that no other skin can hope to have. The skin is the Mystique cosmetic that's part of the battle pass, and its ability allows players to transform themselves into a character that they recently eliminated. You'll maintain that look for as long as you want, but you can also go back to your previous form at any point by repeating the emote used to copy others' appearances.
The Mystique skin is one that's tucked away deep in the battle pass in the 86th tier, so it may be a while before many players are able to experience it themselves. For those who won't be able to get it for a while, the video below from Ben Walker shows what the transformation process looks like.
While wearing the default Mystique skin, you can eliminate people and then go to your emote wheel to find the "Shapeshifter" emote. Using that will have Mystique hold a skull and transform into the skin that she just eliminated. You can perform your normal actions like movements and emotes like you typically would afterwards, and emoting again will transform you back to your Mystique skin.
That Shapeshifter emote is exclusive to the Mystique skin itself which limits the transformation feature to Mystique alone.
Mystique's cosmetic feature shouldn't impact gameplay at all, but it looks like other powers tied to different heroes will have more of an effect later in the season. We've seen hints of a Black Panther suit that can cause an explosion to inflict absorbed damage back onto enemies, and Epic Games has already teased other powers connected to certain heroes.
"You now have the power. Take up super-powers like Doctor Doom's Arcane Gauntlets, Groot's Bramble Shield, Silver Surfer's Board, and more arriving later in the season," Epic Games said in its preview of the current season.
Mystique's skin is also just one of many different Marvel skins that have been added to the game for the current season. Most of the cosmetics and their alternate styles are unlocked within the battle pass while Wolverine's cosmetic is earned by completing challenges.