Reaper King + Purity + Atla Palani, Nest Tender + Maskwood Nexus

Reaper King

Purity

Atla Palani, Nest Tender

Maskwood Nexus

How it works

1. Cause a creature to enter the battlefield under your control by any method.
2. When that creature enters the battlefield, Reaper King triggers, destroying that creature.
3. Resolve Atla Palani's trigger, revealing cards from the top of your library until you reveal a creature card and putting it onto the battlefield.
4. Repeat from step 2 until Purity enters the battlefield then dies, or until you choose to end the loop by destroying an opponent's permanent.
5. If Purity dies, it and Atla Palani trigger.
6. Resolve Purity's trigger, shuffling it into your library.
7. Continue from step 3.

Maskwood Nexus is the true engine here, quietly turning every creature you own and create into a Scarecrow, an Egg, and every other creature type simultaneously. This universal typing means that whenever Atla Palani, Nest Tender hatches an Egg token or reveals a creature into play, Reaper King instantly triggers to destroy it, feeding a self-sustaining loop of endless creature deaths and enters-the-battlefield effects. Because Purity possesses a built-in replacement effect that shuffles itself back into your library whenever it hits the graveyard, you never have to worry about decking yourself while churning through your entire deck's worth of creatures.