[This could almost be a natural cave pool, and maybe it was once. Now all the water has been saturated with blood, and glows a dull, sickly red. There’s a mad tangle of talismans and twine all around it and dangling partially into it, which look to have snapped and fallen from the cave ceiling. Some sort of broken barrier…?

tl;dr it is absolutely the canon blood pool

There are flickering, strange presences darting and congregating thickly under the liquid.

His instincts don’t scream danger just looking down into the pool, but they do twinge. It’s risky to deal with whatever’s in there.]