Cast Traveling Plague by paying 3, attaching it to another creature you control.
When Traveling Plague enters, Archon of Sun's Grace triggers, creating a creature token.
Activate Shilgengar by sacrificing the creature Traveling Plague is attached to.
When the creature dies, Traveling Plague triggers, returning itself from your graveyard to the battlefield attached to the token created in step 2.
When Traveling Plague enters, Archon of Sun's Grace triggers, creating a creature token.
Resolve the Shilgengar ability.
Repeat from step 3.
This fascinating loop turns Traveling Plague into a recursive engine by leveraging its unique trigger: whenever the enchanted creature leaves the battlefield, the Aura returns itself to the battlefield. Shilgengar, Sire of Famine provides the sacrifice outlet to trigger this loop while generating Blood tokens, and Archon of Sun's Grace acts as the constant catalyst by watching enchantments enter the battlefield to pump out a steady stream of Pegasus tokens for Shilgengar to consume. Because Traveling Plague can reattach directly to each newly minted Pegasus token, you can endlessly cycle the Aura, rack up sacrifice and death triggers, and flood the board with infinite Blood and creature tokens.