Inexorable Tide + Crystalline Crawler + Gemstone Array + Cavern Harpy

Inexorable Tide

Crystalline Crawler

Gemstone Array

Cavern Harpy

How it works

1. Cast Cavern Harpy by paying .
2. Inexorable Tide triggers, putting a +1/+1 counter on Crystalline Crawler and a charge counter on Gemstone Array.
3. When Cavern Harpy enters the battlefield, it triggers, returning itself from the battlefield to your hand.
4. Activate Gemstone Array's second ability by removing a charge counter from it, adding .
5. Activate Crystalline Crawler's first ability by removing a +1/+1 counter from it, adding .
6. Repeat.

This clever loop spins up infinitely by bouncing Cavern Harpy right back to your hand with its own entrance trigger, fueling your spells with Inexorable Tide in the process. As you recast the Harpy repeatedly, Inexorable Tide triggers on every cast to passively grow your board by proliferating counters onto both Crystalline Crawler and Gemstone Array. Those accumulated counters are then cashed in—Crystalline Crawler's ability converts its +1/+1 counters into mana, while Gemstone Array's charge counters similarly store and filter energy—supplying the exact blue and black mana needed to keep casting the Harpy endlessly.