Mortuary + Bolas's Citadel + Spore Frog + Syr Vondam, Sunstar Exemplar

Mortuary

Bolas's Citadel

Spore Frog

Syr Vondam, Sunstar Exemplar

How it works

1. Activate Spore Frog by sacrificing it.
2. When Spore Frog dies, Mortuary and Syr Vondam trigger.
3. Resolve the Mortuary trigger, putting Spore Frog from your graveyard onto the top of your library.
4. Resolve the Syr Vondam trigger, causing you to gain 1 life and putting a +1/+1 counter on Syr Vondam.
5. Resolve the Spore Frog ability.
6. Cast Spore Frog from the top of your library by paying 1 life.
7. Repeat.

This delightful loop locks down the combat step entirely by weaponizing Spore Frog's self-sacrifice over and over again. Each time the frog hits the graveyard, Mortuary neatly recycles it straight to the top of your library, allowing Bolas's Citadel to let you cast it right back out for a mere single point of life rather than its mana cost. Meanwhile, Syr Vondam, Sunstar Exemplar happily watches the creature die to trigger its own ability, turning every iteration into a free +1/+1 counter and a net-neutral life gain that effortlessly offsets the Citadel's payment.