Derevi, Empyrial Tactician + Cauldron of Souls + Aerith Gainsborough + Ashnod's Altar

Prerequisites

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Steps

1. 1Activate Cauldron of Souls by tapping it, giving Derevi and Aerith persist until end of turn.
2. 2Activate Ashnod's Altar by sacrificing Derevi.
3. 3When Derevi dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
4. 4When Derevi enters the battlefield, it triggers, untapping Cauldron of Souls.
5. 5Activate Ashnod's Altar by sacrificing Aerith.
6. 6When Aerith dies, it triggers twice.
7. 7Resolve Aerith's persist trigger, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
8. 8Resolve the second Aerith trigger, putting a +1/+1 counter on each legendary creature you control, thus removing the -1/-1 counters from Aerith and Derevi.
9. 9Repeat.

Effects

• Infinite +1/+1 counters on legendary creatures you control
• Infinite colorless mana
• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers