I just gave it some thought. I'll be brief:

"Entering" should include "appearing on the board" because then the Pentagram can have a wider range of usefulness. The implication for all other uses of "entering" haven't been considered, but I can safely say that those situations will be more interesting.

The Pentagram should work on spawns, because that would make it more useful. Plus, the stamina cost to hold the Dunwich Horror at bay is quite large. And that's not counting the extra point required to keep the Horror at bay the following upkeep to allow the placer of the Pentagram to get to safety.

When the DH track is full, the Horror is supposed to be place on Sentinel Hill. But with the Pentagram, it cannot be placed on Sentinel Hill. Though in the past I've argued that restrictions ("can't") takes precedence over allowance ("must"). In the same way that Happy Days prevents the terror level from shooting to 10 when you fail The Terrible Experiment, the Dunwich Horror will just have to wait a turn or two to come to town.

okay, sounds good!

Tibs said:

Ah, interesting interpretation of the pentagram. Should be a lot more useful now! So can this cancel riot monsters as well (not just delay the Dunwich Horror)?

I'd say "yeah" But again, they've got a pretty high toughness. But! If you can prevent one of those suckers from coming out, you prevent a BIG monster blocking your way, and possibly another Yellow Sign (my least favorite Blight to draw...)

Yup, you should be allowed to prevent a Riot monster entirely. However, you'd need to get lucky when drawing your Blight, so it's not exactly an exploitable scenario. And "preventing" a monster from appearing isn't the same as "defeating" it, so you should roll for a terror increase for preventing the Riot.

As the townsfolk get increasingly incensed by the editorial and prepare to congregate in (Northside streets), they see that someone has drawn a pentagram, in blood, in the middle of the street, and decide it might be better to stay home that evening.

Tibs said:

Oh geez, now I'm confused again. The roll to determine if the terror increases only occurs when a Riot is defeated (i.e., a combat check is made against it). If a Riot is prevented, it's not defeated, so we wouldn't roll for a terror increase, right?

Oops, I just noticed that the Riot monster specifies that its effect occurs when you pass a Combat check against it. Which is not what the Pentagram does, so there's that.

But, mechanically, "defeats" is identical to "passes a combat check against." So if you ever see the word "defeat" in relationship to a monster token, whether as a pre-requisite or an effect or an award, replace that term with "pass a combat check against."