I assume you are talking about Heavens Wrath.  It is an Assasin Favor item.  You need to click on the tab to go from basic favor items to General/Assasin Favor items.

It actually took me awhile to figure this out when I was new to the game.

The same thing works for general (as in assassin/general) items.  If you are a general, you have to click on the 2nd tab when you select a favor item to get general only favor. 

The other two good favor items on that menu are Poison Dagger, Blade of the Serpent, and Staff of Renewal.

[quote who="[ShakeNBake]" reply="6" id="2386935"]
two

Poison Dagger, Blade of the Serpent, and Staff of Renewal

i lol'd[/quote]

me too!

Bah, I was only going to put down Poison Dagger and BotS, but then I remembered Staff of Renewal.