The name of the item is an allusion to the Church of Zathroth. The Dark Trinity (Archpriest and two Tribunes) is its highest commission. Therefore, you might expect this weapon to appear as loot from further powerful demon bosses yet to appear in game.
It was implemented in the Update 8.2 and can currently be seen in Pythius The Rotten's treasure room; however, the mace is being covered by a Green Gem.
Before gamemasters were dismissed, CipSoft gave them a list of items to choose as a token of their appreciation and this is one of the items that were on this list. On August 9, 2010, Pytru (GM Havey) created a thread with an auction on a Solar Axe, a Dark Trinity Mace or The Epiphany (the highest bidder decides what item it will be). The thread can be found here. In same way, is the thread created by GM Aestyn, it can be found here.