Cast Basking Broodscale by paying {1}{G}.
Activate Basking Broodscale's adapt ability by paying {1}{G}, putting a +1/+1 counter on it.
Basking Broodscale triggers, creating a 0/1 Eldrazi Spawn creature token and a Mutagen token due to Donatello.
Activate the Eldrazi Spawn by sacrificing it, adding {C}.
Activate the Mutagen by paying {1}, tapping and sacrificing it, putting a +1/+1 counter on Basking Broodscale.
Repeat from step 3.

Infinite +1/+1 counters on a creature

Infinite ETB

Infinite LTB

Infinite death triggers

Infinite sacrifice triggers

Donatello, the Brains

Basking Broodscale

Put a +1/+1 counter on Scurry Oak.
Scurry Oak triggers, creating a creature token and a Mutagen token due to Donatello.
Activate the Mutagen by paying {0} due to Mutagen Man, tapping and sacrificing it, putting a +1/+1 counter on Scurry Oak.
Repeat from step 2.

Infinite creature tokens

Mutagen Man, Living Ooze

Scurry Oak

Put a +1/+1 counter on Scurry Oak.
Scurry Oak triggers, creating a creature token and a Mutagen token due to Donatello.
Activate Ashnod's Altar by sacrificing the creature token, adding {C}{C}.
Activate the Mutagen by paying {1}, tapping and sacrificing it, putting a +1/+1 counter on Scurry Oak.
Repeat from step 2.

Infinite colorless mana

Ashnod's Altar

Activate Summoning Station by tapping it, creating a 2/2 Pincher creature token and a Mutagen token due to Donatello.
Activate Krark-Clan Ironworks by sacrificing the Mutagen.
Summoning Station triggers, untapping itself.
Repeat.

Infinite +1/+1 counters on creatures you control

Summoning Station

Krark-Clan Ironworks

Activate a Mutagen by paying {0} due to Mutagen Man, tapping and sacrificing it, putting a +1/+1 counter on Crystalline Crawler.
Animation Module triggers. Holding priority, activate Crystalline Crawler's first ability by removing a +1/+1 counter from it, adding {1}.
Resolve the Animation Module trigger, causing you to pay {1} to create a 1/1 Servo artifact creature token and a Mutagen token.
Repeat.

Animation Module

Crystalline Crawler

Activate a Mutagen by paying {0} due to Mutagen Man, tapping and sacrificing it, putting a +1/+1 counter on Workhorse.
Animation Module triggers. Holding priority, activate Workhorse by removing a +1/+1 counter from it, adding {C}.
Resolve the Animation Module trigger, causing you to pay {1} to create a 1/1 Servo artifact creature token and a Mutagen token.
Repeat.

Workhorse

Activate a Mutagen by paying {0} due to Mutagen Man, tapping and sacrificing it, putting a +1/+1 counter on Berta.
Berta and Animation Module trigger.
Resolve the Berta trigger, adding {1}.
Resolve the Animation Module trigger, causing you to pay {1} to create a 1/1 Servo artifact creature token and a Mutagen token.
Repeat.

Combos with "Donatello, the Brains"