At the beginning of your upkeep, Delaying Shield triggers.
Holding priority, if Delaying Shield has any delay counters on it, activate Vampire Hexmage by sacrificing it, removing all delay counters from Delaying Shield.
Resolve the Delaying Shield ability, doing nothing.
If Vampire Hexmage is in your graveyard, activate Gravewaker by paying 5, returning Vampire Hexmage from your graveyard to your hand.
Repeat.
This clever defense mechanism leverages Delaying Shield to safely intercept any incoming damage as delay counters rather than immediate life loss. By sacrificing Vampire Hexmage during your upkeep, you instantly strip those accumulated counters away before the Shield's upkeep trigger forces you to pay mana or lose life. To keep the cycle going, you then use Gravewaker's activated ability to pull Vampire Hexmage straight out of the graveyard and return it to the battlefield, ready to sacrifice all over again.