Brallin triggers, dealing 1 damage to each opponent and causing you to gain that much life.
Benthic Biomancer triggers, putting a +1/+1 counter on it
Repeat from step 2.
This loop is a brilliantly self-sustaining feedback engine built around incremental triggers that continuously feed each other. By enchanting Brallin, Skyshark Rider with Sunbond, every instance of damage it deals is instantly converted into life-gain, which in turn places +1/+1 counters back onto Brallin. Meanwhile, activating Benthic Biomancer kicks off the discard cycle, which triggers Brallin to deal damage, while Benthic Biomancer's own counter triggers let you loot through your deck endlessly.