Cast Storm Herd by paying {8}{W}{W}, creating a number of 1/1 Pegasus creature tokens equal to your life total.
When the Pegasi enter, Molten Gatekeeper triggers that many times, dealing that much damage to each opponent.

Near-infinite ETB

Near-infinite creature tokens

Near-infinite damage

Storm Herd

Molten Gatekeeper

Draw a card.
The Locust God triggers, creating a 1/1 Insect creature token with flying and haste.
The Insect enters the battlefield, triggering Molten Gatekeeper, dealing 1 damage to each opponent.
Curiosity triggers, causing you to draw a card.
Repeat from step 2.

Infinite card draw

Infinite draw triggers

Near-infinite creature tokens with haste

The Locust God

Curiosity

Draw a card.
The Locust God triggers, creating a 1/1 Insect creature token with flying and haste.
When the Insect enters the battlefield, Molten Gatekeeper triggers, dealing 1 damage to each opponent.
Niv-Mizzet triggers, causing you to draw that many cards.
The Locust God triggers for each card drawn this way.
Resolve a trigger, creating a 1/1 Insect creature token with flying and haste.
Repeat from step 3.

Niv-Mizzet, Visionary

Cause a creature to enter the battlefield under your control.
Molten Gatekeeper triggers, dealing 1 damage to each opponent.
The Red Terror triggers, putting a +1/+1 counter on itself.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
When the Servo enters, Molten Gatekeeper triggers.
Holding priority, activate Ashnod's Altar by sacrificing the Servo, adding {C}{C}.
Resolve the Molten Gatekeeper triggers, dealing 1 damage to each opponent.
Repeat from step 3.

Combos with "Molten Gatekeeper"