Workhorse, Mikaeus, the Unhallowed, and Phyrexian Altar

Prerequisites

• Workhorse on the battlefield
• Mikaeus, the Unhallowed on the battlefield
• Phyrexian Altar on the battlefield

Steps

1. Activate Workhorse by removing all +1/+1 counters, adding that many
2. Activate Phyrexian Altar by sacrificing Workhorse, adding one mana of any color
3. Workhorse undying ability triggers, returning it to the battlefield with an additional +1/+1 counter on it
4. Repeat

Results

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