Activate the token Balthor by paying ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) and exiling it, returning all black and red creature cards from your graveyard to the battlefield.
Balthor and Blood Vassal enter the battlefield, triggering Dual Nature's first ability twice.
Resolve the first Dual Nature trigger, creating a token copy of Blood Vassal.
Activate the token Blood Vassal by sacrificing it, adding ({B} magic symbol) ({B} magic symbol) .
Resolve the second Dual Nature trigger, creating a token copy of Balthor.