Cast an Eldrazi with mana value 4, 5 or 6 from your hand by paying its mana cost.
Ulalek and Kozilek's Unsealing's first ability trigger twice, the Eldrazi cast triggers twice if it has a cast ability, Echoes of Eternity triggers once if the Eldrazi cast was colorless.
Resolve the first Ulalek's trigger, causing you to pay {C}{C} to copy the Eldrazi spell, the additional Ulalek's trigger, both Kozilek's Unsealing triggers, both Eldrazi cast triggers if it had one, and the Echoes of Eternity trigger if it triggered.
Resolve both Eldrazi cast triggers, if applicable.
Resolve both Kozilek's Unsealing triggers, creating four 0/1 Eldrazi Spawn creature tokens.
Holding priority, activate two Eldrazi Spawns by sacrificing them, adding {C}{C}.
Resolve the copy of Ulalek's trigger from step 3, causing you to pay {C}{C} to copy the Eldrazi spell, the additional Ulalek's trigger, both Kozilek's Unsealing triggers and any other abilities on the stack.
Repeat from step 4.

Infinite colorless mana

Infinite copies of abilities you control on the stack

Infinite copies of a specific creature

Infinite creature tokens

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Eldrazi Creature Card with MV=4, 5 or 6

Ulalek, Fused Atrocity

Echoes of Eternity

Kozilek's Unsealing

Cast an Eldrazi from your hand by paying its mana cost.
Ulalek triggers, the Eldrazi cast triggers if it has a cast ability, and Kozilek's Unsealing's first ability triggers.
Holding priority, activate Strionic Resonator by paying {2} and tapping it, copying Ulalek's trigger.
Resolve the copy of Ulalek's trigger, causing you to pay {C}{C} to copy the Eldrazi spell, Ulalek's trigger, the Eldrazi cast trigger if it had one, and the Kozilek's Unsealing trigger.
Resolve the Eldrazi cast trigger, if applicable.
Resolve the copy of the Kozilek's Unsealing trigger, creating two 0/1 Eldrazi Spawn creature tokens.
Activate both Eldrazi Spawn creature tokens by sacrificing it, adding {C}{C}.
Resolve the copy of Ulalek's trigger from step 4, causing you to pay {C}{C} to copy the Eldrazi spell, Ulalek's trigger, the Eldrazi cast trigger if it had one, and the Kozilek's Unsealing trigger.
Repeat from step 5.

Strionic Resonator

Cast an Eldrazi from your hand by paying its mana cost.
Ulalek triggers, the Eldrazi cast triggers if it has a cast ability, and Kozilek's Unsealing's first ability triggers.
Holding priority, activate Lithoform Engine's first ability by paying {2} and tapping it, copying Ulalek's trigger.
Resolve the copy of Ulalek's trigger, causing you to pay {C}{C} to copy the Eldrazi spell, Ulalek's trigger, the Eldrazi cast trigger if it had one, and the Kozilek's Unsealing trigger.
Resolve the Eldrazi cast trigger, if applicable.
Resolve the copy of the Kozilek's Unsealing trigger, creating two 0/1 Eldrazi Spawn creature tokens.
Activate both Eldrazi Spawn creature tokens by sacrificing it, adding {C}{C}.
Resolve the copy of Ulalek's trigger from step 4, causing you to pay {C}{C} to copy the Eldrazi spell, Ulalek's trigger, the Eldrazi cast trigger if it had one, and the Kozilek's Unsealing trigger.
Repeat from step 5.

Lithoform Engine

Cast an Eldrazi with mana value 4, 5 or 6 from your hand by paying its mana cost.
Ulalek triggers twice, and Kozilek's Unsealing's first ability triggers once. The Eldrazi cast also triggers if it has a cast ability.
Resolve the first Ulalek's trigger, causing you to pay {C}{C} to copy the Eldrazi spell, Ulalek's trigger, Kozilek's Unsealing's trigger, and the Eldrazi cast trigger if it had one.
Resolve the Eldrazi cast trigger, if applicable.
Resolve the Kozilek's Unsealing trigger, creating two 0/1 Eldrazi Spawn creature tokens.
Holding priority, activate the two Eldrazi Spawns by sacrificing them, adding {C}{C}.
Resolve the copy of Ulalek's trigger from step 3, causing you to pay {C}{C} to copy the Eldrazi spell, Ulalek's trigger, Kozilek's Unsealing's trigger, and the Eldrazi cast trigger if it had one.
Repeat from step 4.

Annie Joins Up

Cast Ancestral Statue by paying {4}.
Kozilek's Unsealing's first ability triggers, creating four 0/1 Eldrazi Spawn creature tokens.
When Ancestral Statue enters the battlefield, it triggers, returning itself from the battlefield to your hand.
Activate the Eldrazi Spawns by sacrificing them, adding {C}{C}{C}{C}.
Repeat.

Infinite storm count

Ancestral Statue

Doubling Season

Cast Ancestral Statue by paying {4}.
Kozilek's Unsealing's first ability triggers, creating two 0/1 Eldrazi Spawn creature tokens.
When Ancestral Statue enters the battlefield, it triggers, returning itself from the battlefield to your hand.
Activate Ashnod's Altar twice by sacrificing the Eldrazi Spawns, adding {C}{C}{C}{C}.
Repeat.

Combos with "Kozilek's Unsealing"