Description from the publisher:
Offered as a promotional reward for backers of the Fate of the Elder Gods Kickstarter.
As the ruler of the Outer Gods, Azathoth's greatness is reflected in the special passive ability of his Dark Gift - Elder Signs only make him more powerful! When serving Azathoth you'll be begging other Cults to visit the Streets of Arkham and send those pesky Investigators your way to Hasten Doom!
(From Kickstarter Update #36:)
About Cult Cards, Azathoth, and the Promotional Monsters
[...] As for Azathoth, you all can feel free to include Az in games of Fate of the Elder Gods. But be warned—Azathoth is intended for advanced play! Azathoth has a very unique passive Dark Gift ability that can be incredibly tricky to control and/or stop if you’re not familiar with how Fate of the Elder Gods plays. We would recommend not including Azathoth in your first couple of games. Later, you’ll find this pesky Elder God a rewarding puzzle to add some variety.