Vat of Rebirth has at least four oil counters on it.
({2} magic symbol) ({B} magic symbol) available.
Steps
Activate Vat of Rebirth by paying ({2} magic symbol) ({B} magic symbol) , tapping it and removing four oil counters from it, returning Myr Battlesphere from your graveyard to the battlefield.
Myr Battlesphere enters the battlefield, creating four 1/1 Myr artifact creature tokens.
Activate Clock of Omens by tapping two Myrs, untapping Vat of Rebirth.
Activate Phyrexian Altar four times by sacrificing Myr Battlesphere and three Myr tokens, adding ({3} magic symbol) ({B} magic symbol) .
Myr Battlesphere and the Myrs die, triggering Vat of Rebirth four times, putting four oil counters on it.