Nether Traitor dies, triggering Sifter of Skulls, crating a 1/1 Eldrazi Scion creature token.
Activate Phyrexian Altar by sacrificing the Eldrazi Scion token, adding one mana of any color.
The Eldrazi Scion dies, triggering Nether Traitor, causing you to pay ({B} magic symbol) to return Nether Traitor from your graveyard to the battlefield.