The Locust God triggers, creating a 1/1 Insect creature token with flying and haste.
When the Insect enters the battlefield,
Impact Tremors triggers, dealing 1 damage to each opponent.
Niv-Mizzet triggers, causing you to draw a number of cards equal to the damage dealt.
Repeat from step 2.
Notes
You must stop the combo at some point before you draw from an empty library to prevent losing the game by accident, assuming an opponent survives until that point.