So, at the time of release in the Dunwich campaign, there's only a handful of cards that this one will apply to:
... and this card is awesome. It makes Blood Pact actually work. Previously, 1 doom for +3 to a test seemed, well, expensive. This would only leave the 'end of agenda' turn to make use of Blood Pact (when further doom wouldn't hurt).
Now, though, go nuts! Blood Pact all over the place. Just hope that you can draw Moonlight Ritual (or better, already have one) before the agenda advances, and then clear it down.
I really like the gambling nature of this combination. It feels like a Faustian pact. Will I draw Moonlight Ritual? Do I wait one more turn and use Blood Pact one more time, risking Ancient Evils, or do I clear it now and struggle with a test?
Brilliant combo, both thematically, and in play.