Jegantha, the Wellspring + Horde of Notions + Hammer of Purphoros + Yahenni, Undying Partisan

Jegantha, the Wellspring

Horde of Notions

Hammer of Purphoros

Yahenni, Undying Partisan

How it works

1. Activate Jegantha by tapping it, adding that cannot be spent to pay generic mana costs.
2. Activate Yahenni by sacrificing Jegantha.
3. Activate Horde of Notions by paying , causing you to cast Jegantha from your graveyard without paying its mana cost.
4. Repeat.

This loop turns Jegantha, the Wellspring into an endlessly recurring sacrifice engine by using its own colored mana production to fuel Horde of Notions' ability, which brings Jegantha right back from the graveyard for free. While the board is already primed with Hammer of Purphoros granting haste so Jegantha can tap the very moment it hits the battlefield, Yahenni, Undying Partisan steps in as the designated executioner to sacrifice Jegantha and simultaneously grow into a massive threat from all the resulting death triggers. Because every iteration completely recycles Jegantha without needing any outside resources, you generate an endless storm count and infinite creature triggers.