This Series Of Hallowed Outfits Could Be A Doorway...

Boss

A doorway to other series of outfits.

I can see it for Killers already...

• Killers actually being made of metal which is hidden under their skin, giving them a robotic feel. And the different Killers would give off that feeling in their own ways, like how Hallowed outfits are doing that. (Like for Wraith, cut wires that spark could stick out of his head instead of the usual bone thingies.)
• Killers that have bonded to an extreme degree with the Entity. Like Entity legs sticking out of their bodies, maybe there are hints of Auric Cells on their bodies.
• Killers that simply look like they've been in the Entity's Realm for a very long time: Ragged clothes, worn-out main weapons, cuts & bruises from the Entity doing some additional torturing.

Reason i don't include Survivor outfits is cause i have none of the Hallowed ones, so i can't really think of similar things.