Well I like also other kind of horror example Aliens (1986), but such a space monster does not include in Forgotten Realms DnD lore.
Umm, one of the two lower-level types of slaad does exactly the chestburster thing. And, actually, gnolls are quite a bit this too, though a bit more indirect (hyena's eat magic-ed corpse and then gnolls burst out of hyenas). Vargouille do something similar with their kiss. And actually the mindflayer tadpoles are also EXACTLY THIS.
Seriously though, I doubt they're going to go the horror route. The protagonists will always be against the odds, but they're always going to have a good chance of victory.
vampires, werewolves, etc... none of that is horror in and of itself... and, in fact, any of the classic horror monsters can be used in tropes like comedy, action, romance, etc...
what makes horror isn't "is there X type of monster" it's isolation, desperation, general feelings of hopelessness, the realization that the world does not work the way you believe it did.
One of the hero elements of I am Legend (the novel which inspired the post-apocalyptic Will Smith movie) was that the guy hunting the vampires in that story ends up learning that the infected people have evolved and regained their sense of self and that HE was the monster terrifying this new breed of person. Because he could go about in the daylight come in and kill them all without them being able to do anything. He was the Grendel... he was the monster. (which is partly why I found the ending of the Will Smith movie irritating... it undermined the whole point of the novel).
