Stalwart Successor + Thunderblust + Yahenni, Undying Partisan

Stalwart Successor

Thunderblust

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Thunderblust
2. When Thunderblust dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. When Thunderblust enters, Stalwart Successor triggers, putting a +1/+1 counter on Thunderblust
4. Resolve the Yahenni ability.
5. Repeat.

This clever loop relies on Yahenni, Undying Partisan's ability to sacrifice Thunderblust, sending it to the graveyard where its persist ability immediately returns it to the battlefield with a -1/-1 counter. As Thunderblust re-enters, Stalwart Successor's triggered ability sees the first counters placed on a creature that turn and responds by putting a +1/+1 counter on Thunderblust. Because Magic's state-based actions cause a +1/+1 counter and a -1/-1 counter to annihilate each other, Thunderblust is left with no counters at all, clearing the way for its persist trigger to fire all over again the next time Yahenni, Undying Partisan demands a sacrifice.