Blightbeetle + Woe Strider + Switcheroo

Blightbeetle

Woe Strider

Switcheroo

How it works

1. Donate Blightbeetle to an opponent
2. Activate Woe Strider by sacrificing the undying creature.
3. When the undying creature dies, its undying ability triggers, returning itself from your graveyard to the battlefield without a +1/+1 counter on it due to Blightbeetle.
4. Resolve the Woe Strider ability.
5. Repeat from step 2.

This clever loop relies on transferring your own Blightbeetle across the table using Switcheroo so its passive ability shuts down your opponent's counters. With that protection lock in place, you can feed an undying creature to Woe Strider over and over again; because Blightbeetle prevents +1/+1 counters from being placed on your opponents' creatures, the creature fails to receive its counter upon returning and immediately dies again without resistance. This endlessly repeated cycle generates infinite sacrifice, death, and enter-the-battlefield triggers, all while letting you churn through your library with Woe Strider's repeatable scry ability.