River Song + Kylox's Voltstrider + Walk the Aeons

River Song

Kylox's Voltstrider

Walk the Aeons

How it works

1. Cast Walk the Aeons by paying 4, causing you to take an extra turn after this one.
2. Move to your next turn.
3. Activate Kylox's Voltstrider's first ability by exiling Walk the Aeons from your graveyard, causing Kylox's Voltstrider to become an artifact creature until end of turn.
4. Declare Kylov's Voltstrider as an attacker.
5. Kylox's Voltstrider triggers, causing you to pay 4 to cast Walk the Aeons from exile.
6. Resolve Walk the Aeons, causing you to take an extra turn after this one, and put Walk the Aeons on the bottom of your library.
7. Move to your next turn, drawing Walk the Aeons from the bottom of your library due to River Song.
8. Repeat.

This clever combination creates an infinite extra-turn loop by recycling a single copy of Walk the Aeons straight from the battlefield into your library and back to your hand. Kylox's Voltstrider provides the engine by exiling the sorcery from your graveyard with its collect evidence ability and casting it for free whenever the Vehicle attacks, ultimately tucking the spell onto the bottom of your library rather than letting it hit the graveyard. That is where River Song steps in to completely break the symmetry, altering your draws so that you naturally pull the just-tucked Walk the Aeons right back into your hand on your next draw step to cast it all over again.