Szarel, Genesis Shepherd + Crystalline Crawler + Reassembling Skeleton + Phantom Train

Szarel, Genesis Shepherd

Crystalline Crawler

Reassembling Skeleton

Phantom Train

How it works

1. Activate Reassembling Skeleton by paying 1, returning it from your graveyard to the battlefield.
2. Activate Phantom Train by sacrificing Reassembling Skeleton.
3. When Reassembling Skeleton is sacrificed, Szarel triggers, putting a number of +1/+1 counters equal to Szarel's power on Crystalline Crawler.
4. Resolve the Phantom Train ability.
5. Activate Crystalline Crawler twice by removing two +1/+1 counters from it, adding 1.
6. Repeat.

This loop uses Szarel, Genesis Shepherd to turn the constant recycling of Reassembling Skeleton into a powerful engine for growth and mana generation. By repeatedly casting or returning Reassembling Skeleton from the graveyard using Szarel's ability to play lands and its sacrifice payload, you feed sacrifices into Phantom Train. Each time Reassembling Skeleton hits the graveyard, Szarel triggers to pile +1/+1 counters onto Crystalline Crawler, whose own ability allows you to strip those counters away for any color of mana—which then funds the next iteration of Reassembling Skeleton's return.