From Fantasy Flight's website :

"Know, O Thief, that these things are mine. For I am the Dark Pharaoh, him of the Crawling Chaos. Take what is mine and your blood will boil in your skin. As I reveal to you my Other Faces and my True Glory."

This is an official Herald, published by Fantasy Flight Games (originally only on the website, later also in Arkham Horror: The Curse of the Dark Pharaoh Expansion (Revised Edition)), to be used when using the Herald / Guardian mechanic in games of "Arkham Horror".

Rules Summary :

When the Dark Pharaoh is the Herald, place the Dark Pharaoh monster token in the monster cup at the start of the game even if Nyarlathotep is not the Ancient One.

Know O'Thief : Each time an investigator gains a Unique item (including starting equipment) that investigator loses 1 sanity.

These Things are Mine : Each time an investigator gains an Exhibit item, roll a die. On a failure that investigator is Cursed.

Blood Will Boil : At the start of the Upkeep phase, before rolling for Curses, each Cursed investigator loses 1 stamina.

My Other Faces : All Mask monsters gain 1 toughness. In addition, each time a Mask monster is defeated, add one Doom token to the Ancient One's Doom track.

My True Glory : If Nyarlathotep is the Ancient One and he awakens, his combat modifier increases by 1 (to -5, -6, etc) and he has one extra doom token placed on his doom track (for a total of 12, 13, etc) for each Mask monster on the board.