Activate Spike Feeder's second ability, removing a +1/+1 counter from Spike Feeder and gaining at least 2 life.
Heroic Feast triggers, putting a +1/+1 counter on Spike Feeder.
Repeat.

Infinite lifegain

Infinite lifegain triggers

Spike Feeder

Heroic Feast

Gain life.
Heroic Feast triggers, putting a +1/+1 counter on Scurry Oak
Scurry Oak triggers, creating a creature token.
When the creature token enters the battlefield, Essence Warden triggers, causing you to gain life.
Repeat from step 2.

Infinite +1/+1 counters on a creature

Infinite ETB

Infinite creature tokens

Essence Warden

Scurry Oak

Give Walking Ballista lifelink.
Activate Walking Ballista by removing a +1/+1 counter from it, dealing 1 damage to any target and causing you to gain 1 life.
Heroic Feast triggers, putting a +1/+1 counter on Walking Ballista.
Repeat.

Infinite damage

Walking Ballista

Give Shalai and Hallar lifelink by any method.
Gain life by any method.
Heroic Feast triggers, putting a +1/+1 counter on a creature you control.
Shalai and Hallar triggers, dealing 1 damage to an opponent and causing you to gain at least 1 life.
Repeat from step 2.

Infinite +1/+1 counters on creatures you control

Shalai and Hallar

Gain life.
Heroic Feast triggers, putting a +1/+1 counter on Casey.
Casey triggers, dealing 1 damage to an opponent and causing you to gain 1 life due to its lifelink.
Repeat from step 2.

Casey Jones, Back Alley Brute

Activate Juju Bubble, causing you to gain at least 1 life.
Heroic Feast triggers, putting a +1/+1 counter on Cryptic Trilobite.
Activate Cryptic Trilobite by removing a +1/+1 counter from it, adding at least {2}.
Repeat.

Cryptic Trilobite

Juju Bubble

Gain life.
Heroic Feast triggers, putting a +1/+1 counter on a creature you control.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
When the Servo enters, Virulent Emissary triggers, causing you to gain life.
Heroic Feast triggers. Holding priority, activate Phyrexian Altar by sacrificing the Servo, adding {1}.
Resolve the Heroic Feast trigger, putting a +1/+1 counter on a creature you control 
Repeat from step 3.

Infinite LTB

Infinite death triggers

Infinite sacrifice triggers

Animation Module

Virulent Emissary

Phyrexian Altar

Gain life.
Heroic Feast triggers, putting a +1/+1 counter on Basking Broodscale.
Basking Broodscale triggers, creating a creature token and an artifact token.
When the artifact token enters the battlefield, Teething Wurmlet triggers, causing you to gain life.
Repeat from step 2.

Infinite Food tokens

Infinite card draw

Infinite colorless mana

Infinite draw triggers

Peregrin Took

Basking Broodscale

Teething Wurmlet

Gain life.
Heroic Feast triggers, putting a +1/+1 counter on Fathom Mage.
Fathom Mage triggers, causing you to draw a card.
Horizon Chimera triggers, causing you to gain 1 life.
Repeat from step 2.

Combos with "Heroic Feast"