Yarus, Roar of the Old Gods + Karlov Watchdog + Ashnod's Altar + Switcheroo

Prerequisites

• An opponent controls a creature.
• You control a face-down creature whose front face is a permanent card.
• You have enough mana to cast Switcheroo.

Steps

1. 1Cast Switcheroo by paying its mana cost, giving control of Karlov Watchdog to an opponent.
2. 2During the opponent's turn, activate Ashnod's Altar by sacrificing a face-down creature you control, adding .
3. 3When the creature dies, Yarus's second ability triggers, returning it from your graveyard to the battlefield face-down as a 2/2 creature, and then not turning it face-up due to Karlov Watchdog.
4. 4Repeat from step 2.

Effects

• Infinite colorless mana
• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers