Activate Plaguemaw Beast by tapping it and sacrificing another creature, putting a +1/+1 counter on Scurry Oak.
Scurry Oak triggers, creating a 1/1 Squirrel creature token.
When the Squirrel enters the battlefield, Intruder Alarm triggers, untapping all creatures.
Repeat.

Infinite +1/+1 counters on a creature

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite proliferate

Infinite creature sacrifice triggers

Plaguemaw Beast

Intruder Alarm

Scurry Oak

Activate Plaguemaw Beast by tapping it and sacrificing a creature, causing you to proliferate.
Venser triggers, creating a legendary 3/3 The Hollow Sentinel artifact creature token.
The Hollow Sentinel enters the battlefield, triggering Intruder Alarm, untapping all creatures.
Repeat.

Infinite mana creatures you control can produce

Infinite untap of creatures

Venser, Corpse Puppet

Activate Plaguemaw Beast by tapping it and sacrificing another creature.
When the creature dies, Plaguemaw Beast triggers, untapping itself.
Resolve the Plaguemaw Beast ability, putting a +1/+1 counter on Scurry Oak.
Scurry Oak triggers, creating a 1/1 Squirrel creature token.
Repeat.

Thornbite Staff

Activate Plaguemaw Beast by tapping it and sacrificing a creature.
The creature dies, triggering Plaguemaw Beast, untapping Plaguemaw Beast.
Resolve the Plaguemaw Beast ability from step 1, causing you to proliferate.
Venser triggers, creating a legendary 3/3 The Hollow Sentinel artifact creature token.
Repeat.

Activate Berta by paying {1} and tapping it, creating a 0/0 Fractal creature token and putting a +1/+1 counter on it.
When the Fractal enters, Intruder Alarm triggers, untapping all creatures.
Activate Plaguemaw Beast by tapping it and sacrificing the Fractal, causing you to proliferate and put a +1/+1 counter on Berta.
Berta triggers, adding {1}.
Repeat.

Berta, Wise Extrapolator

Activate Plaguemaw Beast by tapping it and sacrificing another creature.
When the creature dies, Plaguemaw Beast triggers, untapping itself.
Resolve the Plaguemaw Beast ability, putting a +1/+1 counter on Herd Baloth.
Herd Baloth triggers, creating a 4/4 Beast creature token.
Repeat.

Herd Baloth

Activate Plaguemaw Beast by tapping it and sacrificing another creature, putting a +1/+1 counter on Herd Baloth.
Herd Baloth triggers, creating a 4/4 Beast creature token.
When the Beast enters the battlefield, Intruder Alarm triggers, untapping all creatures.
Repeat.

At the beginning of your precombat main phase, There and Back Again triggers, putting a lore counter on it.
There and Back Again's third chapter ability triggers, creating a legendary 6/6 Smaug creature token and causing you to sacrifice There and Back Again.
When Smaug enters the battlefield, Intruder Alarm triggers, untapping all creatures.
Activate Plaguemaw Beast by tapping it and sacrificing Smaug.
When Smaug dies, it triggers, creating fourteen Treasure tokens.
Holding priority, activate five Treasures by tapping and sacrificing them, adding {W}{U}{B}{R}{G}.
Activate Go-Shintai by paying {W}{U}{B}{R}{G} and tapping it, returning There and Back Again from your graveyard to the battlefield with a lore counter on it.
There and Back Again's first chapter ability triggers, causing the Ring to tempt you.
Resolve the Plaguemaw Beast ability from step 4, putting two lore counters on There and Back Again.
There and Back Again's second and third chapter abilities trigger.
Resolve the second There and Back Again trigger, causing you to search your library for a Mountain and put it onto the battlefield.
Resolve the third There and Back Again trigger, creating a legendary 6/6 Smaug creature token and causing you to sacrifice There and Back Again.
Repeat from step 3.

Combos with "Plaguemaw Beast"