Necrotic Ooze + Endling + Walking Ballista + Phyrexian Altar

Necrotic Ooze

Endling

Walking Ballista

Phyrexian Altar

How it works

1. Activate Necrotic Ooze using Endling's third ability by paying , giving Necrotic Ooze undying until end of turn.
2. If Necrotic Ooze has any +1/+1 counters, activate it using Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to any target.
3. Repeat step 2 until Necrotic Ooze has no +1/+1 counters.
4. Activate Phyrexian Altar by sacrificing Necrotic Ooze, adding .
5. Necrotic Ooze dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Repeat.