Cauldron of Souls + Dross Scorpion + Encroaching Mycosynth + Phantom Train

Cauldron of Souls

Dross Scorpion

Encroaching Mycosynth

Phantom Train

How it works

1. Activate Cauldron of Souls by tapping it, giving the creature with bloodthirst persist until end of turn.
2. Activate Phantom Train by sacrificing the creature with bloodthirst.
3. When the creature dies, its persist ability and Dross Scorpion trigger.
4. Resolve the persist trigger, returning the creature from your graveyard to the battlefield, which enters the battlefield with at least one +1/+1 counter on it due to its bloodthirst ability.
5. Resolve the Dross Scorpion trigger, untapping Cauldron of Souls.
6. Resolve the Phantom Train ability
7. Repeat.

This crafty loop turns a simple vehicle into a relentless sacrifice engine, supercharged by the continuous presence of Encroaching Mycosynth which ensures all your permanents are artifacts. That artifact status allows Dross Scorpion to watch your sacrifices and untap Cauldron of Souls every single time a creature bites the dust. Meanwhile, Cauldron of Souls grants persist to your creatures, and Phantom Train happily consumes them to grow larger while neutralizing the -1/-1 counter drawback thanks to the incoming creature's natural +1/+1 counters.