As written this weakness sounds scary (not many weaknesses have the power to instantly defeat an investigator after all), but the insta-kill clause should never fire if you know what you're doing.

Note that the Forced effect only triggers if Gloria actually chooses to use her when looking at the encounter deck. As such, I believe that it is entirely possible for Gloria to simply not use her ability when looking at the deck (e.g. with Parallel Fates (2) which allows reordering), then maneuver a Prophecy of the End to a favorable position (either making sure she gets rid of two at a time with Psychic Sensitivity, or more generally, someone draws it and surges into a card they can handle, making the deck safe until the next reshuffle).
You know how many Prophecies you've eaten, the content of the encounter discard pile is open information and Gloria's should limit you to taking one Prophecy at a time, so you always know whether you are at risk and can plan accordingly.

Regardless, this is still a weakness that can disrupt Gloria's game plan in two significant ways:

1. Obviously, it stops Gloria from discarding dangerous encounter cards or removing them from circulation.
2. Less obviously, as discussed in AlexP's review, Gloria can only take one Prophecy under her if multiple are seen in one , so based on my literal interpretation of the rules, she would have to activate the "if you cannot" clause on the other copy (copies) of Prophecy and release cards into the encounter discard pile earlier than she intended.

On the other hand, a liberal application of the Silver Rule would invalidate everything I've just said, as it can be said that the "it must be chosen" text on each Prophecy takes precedence over Gloria's "choose 1 non-Elite card". In that case she will be forced to take all 3 Prophecies and be instantly defeated if they all show up in a single look.
A ruling may be in order here, but even if this worst-case scenario turns out to be true, Gloria can simply hold back her full Mythos-controlling power for a while until the first Prophecy has shown up and is safely in the discard pile.

Either way, the threat of the Prophecy is mostly intangible - what it can potential do to you stops you from going fully willy-nilly against the encounter deck. This is a design choice I found wonderfully thematic - if I had a nickel for every cosmic horror protagonist that got hurt/mad/traumatized for life/etc. after delving too deep I would be richer than Preston after all. And that's not mentioning the absolutely gorgeous card art, quite possibly my favorite among all released cards so far.

Rules ambiguity and gushing over themes aside, at the end of the day Gloria is a 5 4 Mystic with unparalleled control over the encounter deck, and Prophecy of the End doesn't really do much to change either. This is an interesting and well-designed weakness (certainly way more thought-provoking than Liber Omnium Finium, which in practice often turns out to be nothing more than a repeatable dead draw) that requires some playing around, but I think it's still quite undertuned compared to Gloria's absurd power level.

definitely a card designed with Agatha Crane's ability in mind

playable in either class flavor and desperately wants to played fast

certainly higher player counts encouraged, but even solo its perfectly fine to play for free off her trigger after committing it

Apart from benefitting from Dilemmas, I don't see why George wouldn't want to make the encounter- or his own deck thinner by placing hidden treacheries and weaknesses under him. Heck, some treacheries can even randomly snipe a weakness out of your hand, letting him simply react to it to prevent it from being shuffled back after the deck is empty (which will happen more easily with this investigator).

So long and have fun in Carcosa ;)

EDIT: Transfigurating into George from Patrice Hathaway let's him get rid of the Watcher for good - and that's a guarantee, since in this case Cast Adrift is not in your deck.

Question about this card: If paired with Double, Double, then am I correct that the second instance of Thorough Inquiry would cost an additional 2 resources AND an additional (one) action because of the clause on the card "As an additional cost to play Thorough Inquiry, spend an action"?

If yes, then you would need to have 3 actions available to play a Double, Double'ed Thorough Inquiry.

(also, I'm not sure where to post questions on ArkhamDB. If I'm not supposed to ask questions in reviews, then please tell me where I can post questions. Thanks!) :)

I actually like this card. There are a few scenarios where you want to dig through the encounter deck to find an objective that's hidden near the bottom. Admittedly, that's not many scenarios; certainly not enough to justify taking this card in a vacuum. To be worthwhile, it's going to need extra support--and I'd argue that rather than encounter deck manipulation, what you really want is curse tech.

Although digging for a special location or scenario objective is rare, VP enemies hidden in the encounter deck exist in the vast majority of games. Antediluvian Hymn helps you push those juicy mini-bosses up to the top and add up to 5 to the bag in the process. (Literal bonus points if you find a VP enemy, order it to go to your fighter and then fish it out using Delve Too Deep.)

So who wants this card? No, not Gloria--it fits best with Mystics who use curses to fight:

Dexter Drake armed with Armageddon and Skeptic.

Kōhaku Narukami with Manipulate Destiny and Rod of Carnamagos.

Agatha Crane with Olive McBride and Gaze of Ouraxsh.

...you get the idea. This card isn't Scrying and you're not using it to fail less. It's win-more tech to help you locate what you WANT out of the encounter deck, and the curses you generate are going to help you flatten it when you find it.