Activate Benthic Biomancer by paying 1, putting a +1/+1 counter on it.
Benthic Biomancer triggers, causing you to loot.
Sheoldred triggers, causing you to gain 2 life.
Archangel of Thune triggers, putting a +1/+1 counter on each creature you control.
Repeat from step 2.
This clever loop turns a simple act of adaptation into a self-sustaining engine of life and growth, all fueled by Benthic Biomancer's activated ability. Once that initial counter gets things rolling, the Biomancer's triggered loot causes Sheoldred, the Apocalypse to step in and reward you with a life cushion. That unexpected lifegain instantly wakes up Archangel of Thune, whose static-backed triggered ability blesses your entire board with a fresh crop of +1/+1 counters—which loops right back around to trigger Benthic Biomancer all over again.