(Please note that the image at the top of this article is from Fortnite, which has an Aloy skin.)
A Horizon Forbidden West leak is currently being passed around online, and it's quite fascinating. The footage is apparently from an old alpha build of the open world adventure, showing a four-player multiplayer mode that was, at one point, in development (and probably still is, as pointed out below).
The big talking point, though, is that despite keeping Forbidden West's realistic environments, the character models are very cartoony, immediately drawing comparisons to the designs in games like Fortnite. The leaked video features male and female avatars wearing different clothes and armours, and the characters seem capable of performing the same kinds of sprints and slides as Aloy. However, we don't see the characters engage in any out-and-out combat.
So what happened to this multiplayer project? Well, as far as we know, it's still on the cards. You may remember that late last year, Guerrilla Games was specifically hiring for an online Horizon project featuring "a unique stylized look". This leak is likely the beginnings of that project.