Activate Myr Battlesphere's unearth ability by paying ({1} magic symbol) ({B} magic symbol) ({R} magic symbol) , returning it from your graveyard to the battlefield with haste.
Myr Battlesphere enters the battlefield, creating four 1/1 Myr artifact creature tokens.
Activate Phyrexian Altar three times by sacrificing two Myr tokens and Myr Battlesphere, adding ({1} magic symbol) ({B} magic symbol) ({R} magic symbol) .
Choose to exile Myr Battlesphere using Void Maw's replacement effect instead of its unearth replacement effect.
Activate Void Maw by putting Myr Battlesphere from exile into your graveyard, giving Void Maw +2/+2 until end of turn.