Cast Writhing Chrysalis by paying {2}{R}{G}.
Ulalek and Writhing Chrysalis' first ability triggers twice, and Echoes of Eternity triggers once.
Resolve one of Writhing Chrysalis' triggers, creating two 0/1 Eldrazi Spawn creature tokens.
Resolve the Echoes of Eternity trigger, copying the Writhing Chrysalis spell.
Resolve the copy of the Writhing Chrysalis spell, creating a token copy of it.
Activate both Eldrazi Spawn creature tokens by sacrificing it, adding {C}{C}.
Writhing Chrysalis triggers twice for each Eldrazi sacrificed, putting a total of four +1/+1 counters on itself.
Resolve one of Ulalek's triggers, causing you to pay {C}{C} to copy the Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Resolve the copy of Writhing Chrysalis' trigger, creating two 0/1 Eldrazi Spawn creature tokens.
Activate both Eldrazi Spawn creature tokens by sacrificing it, adding {C}{C}.
Writhing Chrysalis triggers twice for each Eldrazi sacrificed, putting a total of four +1/+1 counters on itself.
Resolve the copy of Ulalek's trigger from step 7, causing you to pay {C}{C} to copy each Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Repeat from step 8 any number of times.
End the combo by letting the stack resolve, putting an infinite number of Writhing Chrysalis tokens onto the battlefield.

Infinite copies of abilities you control on the stack

Infinite creature tokens

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Infinite +1/+1 counters on a creature

Ulalek, Fused Atrocity

Echoes of Eternity

Writhing Chrysalis

Cast Writhing Chrysalis by paying {2}{R}{G}. Ulalek and Writhing Chrysalis' first ability trigger.
Holding priority, cast Eldritch Immunity by paying {C}. 
Ulalek triggers, causing you to pay {C}{C} to copy the Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Resolve the copy of Writhing Chrysalis' 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 Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Repeat from step 4.

Eldritch Immunity

Cast Writhing Chrysalis by paying {2}{R}{G}.
Ulalek and Writhing Chrysalis' first ability trigger.
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 Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Resolve the copy of the Writhing Chrysalis spell.
Resolve the copy of Writhing Chrysalis' trigger, creating two 0/1 Eldrazi Spawn creature tokens.
Activate both Eldrazi Spawn creature tokens by sacrificing it, adding {C}{C}.
Each Writhing Chrysalis you control triggers twice, putting two +1/+1 counters on each of them.
Resolve the copy of Ulalek's trigger from step 4, causing you to pay {C}{C} to copy the Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Repeat from step 5.

Infinite +1/+1 counters on an infinite number of creature tokens

Infinite colorless mana

Strionic Resonator

Cast Writhing Chrysalis by paying {2}{R}{G}.
Ulalek and Writhing Chrysalis' first ability trigger.
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 Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Resolve the copy of the Writhing Chrysalis spell.
Resolve the copy of Writhing Chrysalis' trigger, creating two 0/1 Eldrazi Spawn creature tokens.
Activate both Eldrazi Spawn creature tokens by sacrificing it, adding {C}{C}.
Each Writhing Chrysalis you control triggers twice, putting two +1/+1 counters on each of them.
Resolve the copy of Ulalek's trigger from step 4, causing you to pay {C}{C} to copy the Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Repeat from step 5.

Lithoform Engine

Cast Writhing Chrysalis by paying {2}{R}{G}. Ulalek and Writhing Chrysalis' first ability trigger.
Holding priority, cast Nameless Inversion by paying {1}{B}
Ulalek triggers, causing you to pay {C}{C} to copy the Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Resolve the copy of Writhing Chrysalis' 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 Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Repeat from step 4.

Nameless Inversion

Cast Writhing Chrysalis by paying {2}{R}{G}.
Ulalek triggers twice, and Writhing Chrysalis' first ability triggers once.
Resolve one of Ulalek's triggers, causing you to pay {C}{C} to copy the Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Resolve the copy of Writhing Chrysalis' 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 3, causing you to pay {C}{C} to copy the Writhing Chrysalis spell, Ulalek's trigger and Writhing Chrysalis' trigger.
Repeat from step 4.

Combos with "Writhing Chrysalis"