When Yawgmoth enters the battlefield, Answered Prayers and Scurry Oak's evolve ability trigger.
Holding priority, activate Yawgmoth by paying 1 life and sacrificing a creature, putting a -1/-1 counter on Scurry Oak and causing you to draw a card.
Resolve the Answered Prayers trigger, causing you to gain 1 life.
Resolve the Scurry Oak trigger, putting a +1/+1 counter on it, triggering Scurry Oak's second ability.
Holding priority, activate Yawgmoth by paying 1 life and sacrificing a creature, putting a -1/-1 counter on Scurry Oak and causing you to draw a card.
Resolve the Scurry Oak trigger, creating a 1/1 Squirrel creature token.
When the Squirrel enters the battlefield, Answered Prayers and Scurry Oak's evolve ability trigger.
Repeat from step 4.
This clever loop turns the cycle of life and death into an endless engine, fueled by Yawgmoth, Thran Physician sacrificing your creatures to draw cards and distribute -1/-1 counters. Scurry Oak acts as the heart of the loop, producing a 1/1 green Squirrel creature token whenever it receives a +1/+1 counter from its own evolve ability, which instantly replaces the sacrificed material. Meanwhile, Answered Prayers quietly anchors the math by converting every incoming creature into a steady stream of lifegain, ensuring you never run out of the life resources needed to keep Yawgmoth's scalpel working.