Blightbeetle + Phyrexian Altar + Switcheroo

Blightbeetle

Phyrexian Altar

Switcheroo

How it works

1. Donate Blightbeetle to an opponent
2. Activate Phyrexian Altar 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. Repeat from step 2.

This clever loop relies on *Switcheroo* to donate Blightbeetle to your unsuspecting opponent, shutting down their ability to place +1/+1 counters. Once Blightbeetle is firmly on the other side of the battlefield, you can endlessly loop an undying creature using *Phyrexian Altar* for sacrifice. Normally, undying would return the creature with a counter to prevent infinite recursion, but Blightbeetle's passive protection completely bypasses that restriction. The result is a seamless engine that churns out infinite colored mana alongside endless death, sacrifice, and creature entry triggers.