Reversed monsters.

it's also the reverse of a blog post in that it's bad and not good

Skeletons Skin husks: Skin husks are big floating skins of people, monsters, and animals. They move like those leaves you see drifting on the wind, in that they drift on the wind. They are shockingly light, much lighter than skins actually are. They attempt to wrap around your body, and slowly move themselves over your skin. If you don't fit, it will stretch/crush you until it fits snugly around.

Ghoul Incubator. Looks only somewhat humanoid, with a huge barrel chest about twice the size of a normal torso, tiny vestigial arms, and hundreds of tiny legs. It has no head, instead it's neck ending in a large flared hole big enough to push a melon through. It's full of a thick yellowish liquid that sloshes when it walks, and it is not particularly hostile. If you throw in anything human, such as a hair or fingertip, it creates a whole, new person out of it over the course of the next 1d6 minutes, and vomits them out through it's neck hole. After it does this, it's yellowish fluid is depleted, and it must spend 1d6 weeks replenishing it. 

Roper Unspooler. A large, blobby thing with large, blobby appendages that more resemble big bags of frosting than arms or fins. It drops from ceilings or sits by doors to get a big blobby blorp in before anyone notices. Once you are blorped, your body begins to lose cohesion and tightness. Your eyes begin to roll out of your sockets if you don't keep them in, you skin slowly peels itself off like a loose coat in the wind, and you come apart. This process can be cured by applying significant pressure to the afflicted area or by remaining still and waiting out the toxin/curse. The creature will prioritize eating unspooled bodies over fighting spooled enemies, and as soon as it eats it shits a whole bunch of eggs and dies. 

Ochre Jelly Green Steel. A lump of green or blue metal, sitting motionless. It is capable of vibrating, changing how well it conducts heat or electricity, and of communicating telepathically with anyone touching it. It is about as smart and charismatic as a mind flayer. It most likely has warning labels and beware signs from whoever put it where it is, but it will act unconcerned about these. It's intent is to kill the players. It's only mental stimulation is killing people . It will be cunning and violent. Watch death note or osmosis jones to get a good idea of what we're looking at here.

Green Slime Reversal Rat. A large furry rat. There are usually several, and each is about 30 pounds. They are not a particularly difficult enemy, swarming mindlessly in most fights with it's only real tactic being ambush. However, Players will find odd, impossible bones near swarms of them, including ogre bones the size of small children, and roper bones without any sockets for the rope tentacles. When something is killed by a reversal rat, it turns into the opposite of itself and regains all it's health. Reversal rats have a venom that only affects reversed creatures, allowing them to quickly swarm the resurrected enemy and overwhelm them.