Battlemage's Bracers + Heronblade Elite + Seeker of Skybreak

Battlemage's Bracers

Heronblade Elite

Seeker of Skybreak

How it works

1. Activate Heronblade Elite by tapping it, adding at least two mana of any color
2. Activate Seeker of Skybreak by tapping it, targeting Heronblade Elite.
3. Battlemage's Bracers triggers, causing you to pay 1 to copy Seeker of Skybreak's ability, targeting Seeker of Skybreak.
4. Resolve both Seeker of Skybreak abilities, untapping it and Heronblade Elite.
5. Repeat.

This clever loop relies on Seeker of Skybreak to continually untap Heronblade Elite, which is equipped with Battlemage's Bracers to copy the untap ability so both creatures stay ready for action. As Heronblade Elite grows from humans entering the battlefield, its mana-producing tap ability scales up, easily paying the copy cost required by Battlemage's Bracers while generating an endless surplus of colored mana. By alternating the targets of Seeker of Skybreak's copied and original activations, you keep the entire engine running indefinitely.