Kentaro, the Smiling Cat + Cavern Harpy + Urza's Incubator + Arcane Adaptation

Kentaro, the Smiling Cat

Cavern Harpy

Urza's Incubator

Arcane Adaptation

How it works

1. Cast Cavern Harpy by paying 0.
2. When Cavern Harpy enters the battlefield, it triggers, returning itself from the battlefield to your hand.
3. Repeat.

By using Arcane Adaptation to name Samurai as the chosen creature type, every creature you control and cast falls under that umbrella, including Cavern Harpy. Urza's Incubator steps in to slash the casting cost of those Samurai spells by {2}, a discount that combines perfectly with Kentaro, the Smiling Cat's static ability allowing you to pay {X}—in this case, zero—rather than the mana cost for your Samurai spells. This leaves you free to repeatedly cast Cavern Harpy for zero mana, letting its own enters-the-battlefield trigger bounce it right back to your hand for an endless loop of entries, leaves, and storm count.