Sensei's Divining Top + Skyswimmer Koi + Temur Battlecrier

Sensei's Divining Top

Skyswimmer Koi

Temur Battlecrier

How it works

1. Cast Sensei's Divining Top by paying 0 due to Temur Battlecrier.
2. When Sensei's Divining Top enters, Skyswimmer Koi triggers.
3. Holding priority, activate Sensei's Divining Top by tapping it, causing you to draw a card and put Sensei's Divining Top on top of your library.
4. Resolve the Skyswimmer Koi trigger, causing you to draw Sensei's Divining Top from your library, and then discard a card other than Sensei's Divining Top.
5. Repeat

This clever loop relies on Temur Battlecrier to reduce the cost of Sensei's Divining Top down to zero, allowing you to cast it completely for free. Once it enters the battlefield, Skyswimmer Koi triggers to let you draw and discard, but you can respond by tapping the Top itself to draw a card and place it safely back on top of your library. When the Koi's trigger finally resolves, you draw the Top right back out of your library, primed to be recast for zero mana all over again.