Activate Yawgmoth's first ability by paying 1 life and sacrificing another creature, 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.
When the Insect enters the battlefield, Impassioned Orator triggers, causing you to gain 1 life.