Activate Viscera Seer by sacrificing Marionette Master.
When Marionette Master dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When Marionette Master enters, its fabricate ability triggers, putting a +1/+1 counter on it.
Resolve the Viscera Seer ability.
Repeat.
This elegant loop relies on Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight granting its persist ability to Marionette Master, allowing the Master to return from the graveyard with a -1/-1 counter whenever it dies to Viscera Seer. Marionette Master’s fabricate ability counters this drawback upon re-entry by placing a +1/+1 counter on it, which immediately neutralizes the -1/-1 counter through state-based actions. Meanwhile, Marionette Master's own triggered ability weaponizes the entire cycle, draining life from your opponents each time it hits the graveyard as an artifact creature.