Cast Sprout Swarm with buyback by paying at most {4}{G}.
Witch-Maw Nephilim's first ability triggers, putting two +1/+1 counters on it.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
Activate Ashnod's Altar by sacrificing the Servo, adding {C}{C}.
When the Servo dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Activate the Treasure by tapping and sacrificing it, adding {1}.
Resolve Sprout Swarm, creating a 1/1 Saproling creature token and returning Sprout Swarm to your hand.
Cast Sprout Swarm by paying {4} and tapping the Saproling token.
Witch-Maw Nephilim's first ability triggers; holding priority, activate Ashnod's Altar by sacrificing the Saproling, adding {C}{C}.
When the Saproling dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve the Witch-Maw Nephilim trigger, putting two +1/+1 counters on it.
Repeat from step 3.
Once you have infinite mana, you may forego sacrificing the Servos and/or the Saprolings.

Infinite +1/+1 counters on Witch-Maw Nephilim

Infinite colored mana

Infinite colorless mana

Infinite creature tokens

Infinite death triggers

Infinite ETB

Infinite LTB

Infinite magecraft triggers

Infinite sacrifice triggers

Infinite storm count

Infinite Treasure tokens

Witch-Maw Nephilim

Animation Module

Pitiless Plunderer

Sprout Swarm

Ashnod's Altar

Cast Wurmcalling with buyback by paying {3}{G}{G}.
Witch-Maw Nephilim's first ability triggers, putting two +1/+1 counters on it.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
Activate Ashnod's Altar by sacrificing the Servo, adding {C}{C}.
When the Servo dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve Wurmcalling, creating a 1/1 Wurm creature token and returning Wurmcalling to your hand.
Activate Ashnod's Altar by sacrificing the Wurm, adding {C}{C}.
When the Wurm dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Activate the Treasures by tapping and sacrificing them, adding {G}{G}.
Repeat.

Wurmcalling

Cast Lab Rats with buyback by paying {4}{B}.
Witch-Maw Nephilim's first ability triggers, putting two +1/+1 counters on it.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
Activate Ashnod's Altar by sacrificing the Servo, adding {C}{C}.
When the Servo dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve Lab Rats, creating a 1/1 Rat creature token and returning Lab Rats to your hand.
Activate Ashnod's Altar by sacrificing the Rat, adding {C}{C}.
When the Rat dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Activate the Treasures by tapping and sacrificing them, adding {1}{B}.
Repeat.

Lab Rats

Cast Recruit the Worthy with buyback by paying {3}{W}.
Witch-Maw Nephilim's first ability triggers, putting two +1/+1 counters on it.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
Activate Ashnod's Altar by sacrificing the Servo, adding {C}{C}.
When the Servo dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve Recruit the Worthy, creating a 1/1 Soldier creature token and returning Recruit the Worthy to your hand.
Activate Ashnod's Altar by sacrificing the Soldier, adding {C}{C}.
When the Soldier dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Activate a Treasure by tapping and sacrificing it, adding {W}.
Repeat.
Once you have infinite Treasure tokens, you may forego sacrificing the Servos and/or Soldiers.

Recruit the Worthy

Cast Clockspinning with buyback by paying {3}{U}, targeting Witch-Maw Nephilim.
Witch-Maw Nephilim's first ability triggers, putting two +1/+1 counters on it.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
Activate Krark-Clan Ironworks by sacrificing the Servo, adding {C}{C}.
When the Servo dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve Clockspinning, putting a +1/+1 counter on Witch-Maw Nephilim and returning Clockspinning to your hand.
Repeat steps 3 through 5 one additional time.
Activate the Treasures by tapping and sacrificing them, adding {1}{U}.
Repeat.
You may also target any other creature you control that has a +1/+1 counter on it using Clockspinning.

Infinite +1/+1 counters on creatures you control that have a +1/+1 counter on them

Clockspinning

Krark-Clan Ironworks

Cast Clockspinning with buyback by paying {3}{U}, targeting Witch-Maw Nephilim.
Witch-Maw Nephilim's first ability triggers, putting two +1/+1 counters on it.
Animation Module triggers, causing you to pay {1} to create a 1/1 Servo artifact creature token.
Activate Ashnod's Altar by sacrificing the Servo, adding {C}{C}.
When the Servo dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve Clockspinning, putting a +1/+1 counter on Witch-Maw Nephilim and returning Clockspinning to your hand.
Repeat steps 3 through 5 one additional time.
Activate the Treasures by tapping and sacrificing them, adding {1}{U}.
Repeat.
You may also target any other creature you control that has a +1/+1 counter on it using Clockspinning.

Combos with "Witch-Maw Nephilim"