Timestream Navigator + Molten Echoes + Crystal Shard

Timestream Navigator

Molten Echoes

Crystal Shard

How it works

1. Cast Timestream Navigator by paying 1.
2. If you don't have the city's blessing and control ten or more permanents, Timestream Navigator gives you the city's blessing.
3. When Timestream Navigator enters the battlefield, Molten Echoes triggers, creating a token copy of Timestream Navigator with haste.
4. If you don't have the city's blessing, the Timestream Navigator token gives you the city's blessing.
5. Activate Crystal Shard by paying 3 or and tapping it, returning the nontoken Timestream Navigator to your hand from the battlefield.
6. Activate the Timestream Navigator token by paying 2, tapping it and putting it on the bottom of your library from the battlefield, causing you to take an extra turn after this one.
7. Repeat each turn.

This clever engine achieves infinite turns by continuously recycling Timestream Navigator with the help of Molten Echoes and Crystal Shard. As you cast and recast Timestream Navigator, Molten Echoes ensures a fresh copy enters the battlefield every turn to leverage the city's blessing, while Crystal Shard safely bounces the original back to your hand so you can replay it. With the token sacrificing itself to its own activated ability for the extra turn, you loop the sequence indefinitely to lock down the game.