Your cryptid fear ideas are fantastic. Also Sirens as the web is actually fantastic. They work for the buried with drowning or slaughter with the hypnotic music, but at the core the web just feels right.
Thank you! Sirens in general are just made to be TMA entities, they line up with all of them so well.
Dragging sailors to the depth’s of the sea? That’s the buried, the vast, the desolation, the slaughter, and the end all wrapped up into one.
Luring sailors in with hypnotic music, good looks, and sometimes acts of peril? That could very well be connected to the web, the hunt, the spiral, the lonely, or the stranger.
Being half-human and half-fish? That could be flesh or corruption coded. Luring in sailors during storms? The dark. Watching sailors from afar? The eye. Connected to doomed voyages? The extinction.
Something I find really fun about the entities actually is the fact that you can spend so much time thinking about where certain things would fall in the TMA universe. Like, yes, I do believe that sirens would fall under the web and bigfoot would belong to the lonely. That thought process came free with my Magnus Archive subscription.