Mairsil, the Pretender, Endling, Blood Vassal, and Crystalline Crawler

Prerequisites

• Mairsil on the battlefield
• All other cards exiled with cage counters on them
• Mairsil does not have a +1/+1 counter on it
• available

Steps

1. Activate Mairsil using Endling's third ability by paying , giving Mairsil undying until end of turn
2. Activate Mairsil using Blood Vassal's ability by sacrificing it, adding
3. Mairsil dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it
4. Activate Mairsil using Crystalline Crawler's first ability by removing a +1/+1 counter from it, adding one mana of any color
5. Repeat

Results

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