Inexorable Tide + Crystalline Crawler + Pentad Prism + Cavern Harpy

Inexorable Tide

Crystalline Crawler

Pentad Prism

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 Pentad Prism.
3. When Cavern Harpy enters the battlefield, it triggers, returning itself from the battlefield to your hand.
4. Activate Pentad Prism 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.