Muldrotha, the Gravetide + Timestream Navigator + Riptide Shapeshifter

Muldrotha, the Gravetide

Timestream Navigator

Riptide Shapeshifter

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 loop grants you infinite turns by recycling Timestream Navigator, which tucks itself into your library to secure an extra turn once you have the city's blessing. To find it again, Riptide Shapeshifter is sacrificed to search your library and put Timestream Navigator right back onto the battlefield. Because Muldrotha, the Gravetide allows you to cast a permanent spell of each type from your graveyard during your turn, you can easily replay Riptide Shapeshifter from your graveyard on each of your extra turns to restart the cycle.