The possibility of taking Efren down from 33 life to zero seems unlikely; you don’t have enough damage on the table to do that. Poison counters would probably be the best route, but your Core Prowler can’t attack, your Priests of Norn have zero power, and you simply don’t have any other creatures that can poison your opponent. Fortunately, you’ve got a card that can let them do so: Grafted Exoskeleton. You’ll need to take a little initative, though…
- Tap two forests to add GG (both used as generic mana) to your mana pool.
- Spend 2 to equip Grafted Exoskeleton to your Mycosynth Fiend. Your Mycosynth Fiend is now a 4/4 creature with infect. Because Grafted Exoskeleton became unattached from Perilous Myr, you must sacrifice Perilous Myr.
- Perilous Myr’s ability triggers. Choose to have Perilous Myr deal 2 damage to Efren’s Suture Priest, destroying it. (Efren’s Darksteel Axe becomes unattached.)
- Declare the start of your combat phase, assigning your Priests of Norn, Mycosynth Fiend, and Viridian Betrayers to attack.
- Tap one plains to add W to your mana pool.
- Spend W to cast Seize the Initiative on your Priests of Norn. Priests of Norn is now a 1/4 creature with first strike.
- Efren has no untapped creatures, and is therefore unable to block any of your attackers.
- Because Priests of Norn has first strike, it deals 1 damage to Efren during the first strike damage step. This gives Efren one poison counter. As a result, Mycosynth Fiend is now a 5/5 creature, and Viridian Betrayers now has infect.
- Mycosynth Fiend and Viridian Betrayers deal a total of 8 damage to Efren. This gives Efren eight poison counters, for a total of nine poison counters.
- During your second main phase, tap one forest to add G (used as generic mana) to your mana pool.
- Spend 1 and tap your Phyrexia’s Core to activate its ability, sacrificing your Core Prowler. You gain 1 life. You are now at 2 life.
- Core Prowler’s ability triggers, allowing you to proliferate. Choose to give Efren a tenth poison counter, defeating him.