Ratadrabik of Urborg + Sarkhan, the Dragonspeaker + Yahenni, Undying Partisan

Ratadrabik of Urborg

Sarkhan, the Dragonspeaker

Yahenni, Undying Partisan

How it works

1. Activate Sarkhan's first loyalty ability by putting a loyalty counter on it, causing it to become a legendary 4/4 Dragon creature with flying, indestructible and haste.
2. Activate Yahenni by sacrificing Sarkhan.
3. When Sarkhan dies, Ratadrabik triggers, creating a token copy of Sarkhan that isn't legendary.
4. Resolve the Yahenni ability.
5. Repeat using the Sarkhan token.

This clever loop turns the planeswalker Sarkhan, the Dragonspeaker into a self-replicating engine by using his +1 ability to temporarily make himself a legendary creature. Because Ratadrabik of Urborg sees this legendary creature die when sacrificed to Yahenni, Undying Partisan's ability, it triggers to create a nonlegendary token copy of Sarkhan. That token can immediately activate its own loyalty ability to become a creature again, allowing Yahenni to sacrifice it ad infinitum.