Kentaro, the Smiling Cat + Kor Skyfisher + Urza's Incubator + Arcane Adaptation

Kentaro, the Smiling Cat

Kor Skyfisher

Urza's Incubator

Arcane Adaptation

How it works

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

By naming Samurai with both Urza's Incubator and Arcane Adaptation, every creature you cast becomes a Samurai and enjoys a massive two-mana discount. This reduction dovetails perfectly with Kentaro, the Smiling Cat, whose static ability lets you pay {X} rather than a spell's mana cost using that exact value—meaning your creatures now effectively cost zero to cast. When you cast Kor Skyfisher for free, its enter-the-battlefield trigger forces you to return a permanent to your hand, which conveniently picks up the very same Kor Skyfisher so you can loop the process indefinitely.