Activate Yawgmoth's first ability by paying 1 life and sacrificing another creature.
When the creature dies, Dross Harvester's second ability triggers, causing you to gain 2 life.
Resolve the Yawgmoth ability, causing you to draw a card and allowing you to put a -1/-1 counter on up to one creature.
The Locust God triggers, creating a 1/1 Insect creature token with flying and haste.
Repeat.
This clever loop is fueled by Yawgmoth, Thran Physician, whose sacrifice and card-drawing ability serves as the primary engine for the entire setup. Every time a creature is sent to the graveyard, Dross Harvester steps in to pad your life total, easily offsetting the life payment required to keep Yawgmoth firing. Meanwhile, the mere act of drawing a card causes The Locust God to swoop in with a replacement 1/1 Insect creature token, which can immediately be fed right back into Yawgmoth to perpetuate the cycle indefinitely.