Activate Myr Propagator by paying {3} and tapping it, creating a token copy of it.
When the Myr Propagator token enters the battlefield, Mana Echoes triggers, adding {C} for each Myr you control.
Repeat using the Myr Propagator token instead.

Infinite ETB

Infinite colorless mana

Infinite tapped creature tokens

Myr Propagator

Mana Echoes

Alibou, Ancient Witness

Declare the creature with Breath of Fury attached and Threefold Thunderhulk as attackers.
Threefold Thunderhulk triggers, creating a creature token.
Deal combat damage using the creature that has Breath of Fury attached. 
Breath of Fury triggers, causing you to sacrifice the creature it is attached to, then attach Breath of Fury to the creature token, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Repeat each combat phase.

Infinite LTB

Infinite combat damage

Infinite combat phases

Infinite creature tokens with haste

Infinite death triggers

Infinite mana creatures you control can produce

Infinite sacrifice triggers

Infinite untap of creatures you control

Breath of Fury

Threefold Thunderhulk

Activate Urza by paying {6}, targeting Radiant Lotus.
Locus of Enlightenment triggers, copying Urza's ability, targeting Radiant Lotus.
Resolve both Urza abilities, creating two token copies of Radiant Lotus that are 1/1 Soldier artifact creatures.
Activate a Radiant Lotus token by tapping it and sacrificing both Radiant Lotus tokens, targeting yourself.
Locus of Enlightenment triggers, copying the Radiant Lotus token's ability, targeting yourself.
Resolve both Radiant Lotus abilities, adding twelve mana of any color.
Repeat.

Infinite colored mana

Infinite creature copies of artifacts you control

Infinite creature copies of artifacts you control with haste

Urza, Prince of Kroog

Radiant Lotus

The Enigma Jewel // Locus of Enlightenment

Deal combat damage using the creature that has Breath of Fury attached. 
Breath of Fury and Aya of Alexandria trigger.
Resolve the Aya of Alexandria trigger, creating a 1/1 Assassin creature token.
Resolve the Breath of Fury trigger, causing you to sacrifice the creature it is attached to, then attach Breath of Fury to the Assassin token, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Repeat each combat phase.

Aya of Alexandria

Mycosynth Lattice

Deal combat damage to an opponent using Donatello and the creature that has Breath of Fury attached, triggering Donatello and Breath of Fury.
Resolve the Donatello trigger, creating a token copy of the artifact creature.
Resolve the Breath of Fury trigger, causing you to sacrifice the creature it is attached to, then attach Breath of Fury to the artifact creature token, then causing you to untap all creatures you control and to get an additional combat phase after this one. 
Repeat each combat phase

Donatello, Gadget Master

Activate a creature by tapping it, adding {1}.
The creature's ability granted to it by Tale of Katara and Toph triggers, putting a +1/+1 counter on the creature.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
Repeat.

Tale of Katara and Toph

Animation Module

Song of Freyalise

Combos with "Alibou, Ancient Witness"