If you really want "beast of Satan" territory (imo, Poltys are just very cryptic):

• For behavior, I'm going to appeal to the Brazilian wandering spider which is extremely aggressive, likes to hide in human living spaces, is mobile, and is severely venomous (including causing a painful priapism).
• For prey, going with the Goliath birdeater. I think tarantulas are cute, but this one has the legspan of a fucking dinner plate, weighs up to like a 1/5 of a kilo, has a massive body, has 4 cm fangs, and is large enough to prey on small terrestrial vertebrates.
• For sheer vibes, going with the giant huntsman spider. It lives in caves in Laos, has a legspan of up to 30 cm like the Goliath birdeater (but proportionally smaller body, amplifying the creepiness), was only discovered in 2001 despite being so huge, and as a huntsman is probably fast as fuck. Unsure about the venom; I've never researched it.
• See also: trapdoor spiders.

Not putting any of these images here in case anyone's arachnophobic. Exposure therapy only works if you build yourself up to it, and I don't want anybody to miss out on a chance to come to appreciate spiders.