The Seamstress. A giant snake with a porcelain doll's head that grafts the dead body of 2 onto her tail and uses it to hypnotize 8 into submission, before sewing him inside her body and dragging 7 away and boasts numerous appendages just designed for chopping up and sewing up innocent stitchpunk skin. That thing will haunt my dreams. Also: To silence 8, she sews his mouth shut. Yeah...
That "chopping up innocent stitchpunk skin" echoes the original short, wherein one shot clearly shows part of 5's fabric sewn into the body of the original Beast.
Just watching the Winged Beast's construction is pure nightmare fuel. You see The Fabrication Machine grabbing random bits of scrap, fabric, and human bones, and pull them together off screen. Then a beaked shadow rises up, its eyes light up and it starts screaming.
The fabrication machine approaching timed to Over the Rainbow was particularly haunting.
Anytime someone's soul gets sucked out, but perhaps 5's was the worst, thanks to all his panicked screaming and shouting "No!" over and over again. And the hole burnt in his eyepatch afterwards... brr.
2's was worse, because you didn't know if he was dead or alive, and just had that Pink Floyd The Wall mask look to him.
7 got harpooned for god's sake! and didn't appear to feel any pain, which implies that the stitchpunks can't feel anything, good or bad.
Being a puppet doll means dismemberment won't kill you. Think about it. Also, the soul-stealer.
The whole concept, really; even the cute things are horrifying if you think about them for more than a few seconds. For example, the bird skull that 7 wears for armour is all well and good until you consider that there probably aren't any birds left alive anywhere.
The Cat Beast has a skull strapped onto its head that can give anyone the willies.
Watching 6 get his soul sucked out and his dead body being pitched into a dark, seemingly endless chasm below... *gulp*
Seeing a mother and her baby as withered corpses will never leave this Troper's mind without a good vodka.