Nautico3D's Yellow Rabbit and Springtrap
This version of Afton is probably the most evil he's ever been depicted in any fan-media, and the design for both Yellow Rabbit and Springtrap sells that perfectly.
As Yellow Rabbit, he seems perfectly innocent in a public setting, albeit extremely uncanny, but it's not too bad. When he's killing the kids though, he comes off more like a demonic entity taking the form of a fucked-up version of a cartoon character just to fuck with the kids some more. The way his eyes look like they're looking at two different things yet it's like they're staring into your soul, the way his bottom jaw isn't totally centered, the grin of the mask; it's a perfect design for this version of Springbonnie, as well as this version of Afton.
As Springtrap, he looks fucking terrifying. Here, he's not looking through the mask's eyes. We're seeing Afton's eyes, and it makes him look extremely unsettling. He's permanently slouched over, making him look constantly tense and like he's gonna break into a sprint at any time. His face under the mask is also extremely disturbing, especially with the extra detail of his teeth and how they're placed, looking as if the springlock failure caused his upper teeth to be ripped out of his gums.
Another detail I love is how Nautico3D almost always films Afton at a low angle so he's constantly looking down at you, which adds an extra layer of intimidation to an already terrifying design.
Check out Nautico3D's FNAF animations on his YouTube channel, it's absolutely amazing.