Activate Phyrexian Altar by sacrificing Priest of Gix, adding ({1} magic symbol) .
Activate Epitaph Golem by paying ({2} magic symbol) , putting Priest of Gix on the bottom of your library from your graveyard.
Activate Grenzo by paying ({2} magic symbol) , putting Priest of Gix into your graveyard from the bottom of your library, and then putting it onto the battlefield.
When Priest of Gix enters the battlefield, it triggers, adding ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) .