Necrotic Ooze + Walking Ballista + Phyrexian Devourer

Necrotic Ooze

Walking Ballista

Phyrexian Devourer

How it works

1. Activate Necrotic Ooze's using Phyrexian Devourer's ability by exiling the top card of your library, putting a number of +1/+1 counters on Necrotic Ooze equal to the card's mana value.
2. Repeat step 1 until the number of +1/+1 counters on Necrotic Ooze is at least equal to the sum of your opponents' life totals.
3. Activate Necrotic Ooze using Walking Ballista's last ability by removing a +1/+1 counter from it, dealing 1 damage to any target.
4. Repeat step 3 until all opponents have taken lethal damage.