Mikaeus, the Unhallowed, Cauldron of Souls, Dross Scorpion, and Ashnod's Altar

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Cauldron of Souls on the battlefield
• Dross Scorpion on the battlefield
• Ashnod's Altar on the battlefield

Steps

1. Activate Cauldron of Souls by tapping it, giving Dross Scorpion persist until end of turn
2. Activate Ashnod's Altar by sacrificing Dross Scorpion, adding
3. Dross Scorpion dies, triggering its ability, its undying ability and its persist ability
4. Resolve the first Dross Scorpion trigger, untapping Cauldron of Souls
5. Resolve the Dross Scorpion persist trigger, returning it from your graveyard to the battlefield with a -1/-1 counter on it
6. Activate Ashnod's Altar by sacrificing Dross Scorpion, adding
7. Dross Scorpion dies, triggering its ability and its undying ability
8. Resolve the first Dross Scorpion trigger, untapping Cauldron of Souls
9. Resolve the second Dross Scorpion trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it
10. Activate Ashnod's Altar by sacrificing Dross Scorpion, adding
11. Dross Scorpion dies, triggering its ability and its persist ability
12. Repeat from step 4

Results

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