Timestream Navigator + Riptide Shapeshifter + Karador, Ghost Chieftain

Timestream Navigator

Riptide Shapeshifter

Karador, Ghost Chieftain

How it works

1. Activate Timstream Navigator by paying 2, tapping it and putting it on the bottom of your library, causing you to take an extra turn after this one.
2. Activate Riptide Shapeshifter by paying 2 and sacrificing it, naming any of Timestream Navigator's types, and then revealing Timestream Navigator from your library and putting it onto the battlefield.
3. Move to your next turn.
4. Cast Riptide Shapeshifter from your graveyard by paying 3.
5. Repeat.

This clever loop achieves infinite turns by repeatedly cycling Timestream Navigator straight from the battlefield back into your library and right back out again. Once you have the city's blessing active, Timestream Navigator tucks itself away to grant you an extra turn. From there, Riptide Shapeshifter is sacrificed to fetch that exact same Timestream Navigator back onto the battlefield, ensuring you always have access to its time-bending ability. The engine is then completed by Karador, Ghost Chieftain, whose static ability allows you to cast the Riptide Shapeshifter directly from your graveyard turn after turn, sustaining the loop indefinitely.