Lagrella, the Magpie + Karmic Guide + Preston, the Vanisher + Cloudshift

Lagrella, the Magpie

Karmic Guide

Preston, the Vanisher

Cloudshift

How it works

1. Cast Cloudshift by paying , blinking Lagrella.
2. When Lagrella enters the battlefield, it and Preston triggers.
3. Resolve the Lagrella trigger, exiling Karmic Guide until Lagrella leaves the battlefield.
4. Resolve the Preston trigger, creating a token copy of Lagrella that is a 0/1 Illusion.
5. Put the nontoken Lagrella into your graveyard due to the legend rule.
6. If Lagrella is your commander, choose not to return it to the command zone from your graveyard.
7. When Lagrella leaves the battlefield, Karmic Guide is returned to the battlefield from exile.
8. Karmic Guide, Lagrella and Preston each trigger.
9. Resolve the Preston trigger, creating a token copy of Karmic Guide that is a 0/1 Illusion.
10. When the Karmic Guide token enters the battlefield, it triggers, choosing to return nothing to the battlefield.
11. Resolve the Lagrella trigger, putting two +1/+1 counters on the nontoken Karmic Guide.
12. Resolve the Karmic Guide trigger from step 8, returning Lagrella from your graveyard to the battlefield.
13. Repeat from step 2.

This intricate loop relies on Preston, the Vanisher to multiply your threats by generating 0/1 Illusion token copies whenever a nontoken creature enters the battlefield without being cast. You kick off the engine using Cloudshift to blink Lagrella, the Magpie, triggering both Preston and Lagrella's exile ability to catch Karmic Guide. When the legend rule sends your original Lagrella to the graveyard, Karmic Guide returns to the battlefield and brings Lagrella right back out of the yard, creating a self-sustaining loop that infinitely repeats entering-the-battlefield and leaving-the-battlefield triggers.