You won't notice the stalagmites. Not at first. They don't descend from above, they just.. appear. One moment not, next moment there. Ancient weathered claws grasping the earth. Heron legs or curlicued eagle claws built on titanic scale.
You might hear the crunch as they bite into the ground. Look down where rock meets rock and see the scored and broken stone. Clawed and bunched like a crows feet on a dining table. There are two. One blocks the way ahead, one arrests your flight. You won't see either move on arrival. You will look up. The light will make it impossible not to.
The roof is gone. If it was low enough to see before it isn't now. As if it rose up. Like paperscraps dancing in a lantern flame. The light you carry runs out somewhere in the dark. But there is something else up there. A twice-reflected gleam. Only as bright as the shine of gold in cold vaults. Lead tiles in moonlight. A scratched blackboard bouncing back the streetlamp light refracted in a pane of glass. Illuminating nothing. It is an eye.
You see a figure falling in the dark. Silver-white like a dropped spoon in water-butt. Distant and untouchable as a lake-bottom corpse. A human shape. Far far above you, but deeply held like underwater lights. Falling. Rising. Approaching you like a skydiver with a failed chute. Or like a body rising up out of dark sea into the light. But fast. And direct. Impelled by something.
It looks like you. At first a sliver human-sketch. Then a skeletal cartoon. A formless body. Features. A face. Your face. All resolving as it falls out of the dark. This takes five to three seconds in total.
It breaches the barrier screaming. The dark void-stuff above you shivers and ripples. The silver-feathered-clone-you-thing plunges out of the impossible sky exactly like a spear plunging into a pool. A frothing halo of nought-bubbles slide around it as it comes and then flee upwards. Time and space forming bubbles of reality around something else that will not mix.
It comes down screaming and grabs at you. This would be a good time to fight. It doesn't move like anything attached to this world. It goes up and down in jabs and drops. Like a harpoon seeking river-fish. Like the tip of a weapon. Which is what it is. Grabbing for you. The feathers are knives.
It will become more like you with each stroke. If it succeeds. There will be a flurry of feather-like silver blades. You will be pulled upwards into the darkness to feed the watching horror. Wailing. Your naked evil silver-skinned double will remain. Abandoned. Murderous. Desperate. A Still-Tor-Man.
You can try and fight the stone-like feet that anchor the watching overpredator. They are hard to hurt, quick and massively strong. But while you occupy on or move of them the predator cannot jab its thinking beak into reality to nab you up. They will crush and tear you but at least they won't take you up there.