Silvanus's Invoker + Karoo + Agatha of the Vile Cauldron

Silvanus's Invoker

Karoo

Agatha of the Vile Cauldron

How it works

1. Activate Karoo by tapping it, adding two mana.
2. Activate Silvanus's Invoker by paying 1, untapping Karoo and causing it to become an 8/8 Elemental with trample and haste in addition to its other types until end of turn.
3. Repeat any number of times.
4. Once you have infinite mana, you may tap and untap any other land(s) you control, and if you control lands that can produce and , use the mana to activate Agatha of the Vile Cauldron's ability.

This clever loop turns a modest land into a powerhouse by leaning on Agatha of the Vile Cauldron, whose static ability reduces the activation costs of your creature abilities based on her power. Because that cost reduction makes Silvanus's Invoker cheap enough to activate, tapping Karoo for two mana provides more than enough fuel to pay the reduced activation cost and untap Karoo in return. Repeating this process lets you cycle the land back and forth to generate infinite mana—including the white mana from Karoo—while also unlocking an infinite army of massive, trampling attackers once you funnel that mana into Agatha of the Vile Cauldron's pump ability.