Activate Walking Ballista by removing a +1/+1 counter on it, targeting itself, but putting two +1/+1 counters on it due to Vigor.
Activate Walking Ballista by removing a +1/+1 counter on it, dealing 1 damage to any target.
Repeat.

Infinite +1/+1 counters on creatures you control

Infinite damage

Vigor

Shang-Chi, Martial Mentor

Walking Ballista

Activate Leyline of Abundance by paying {6}{G}{G}, putting four +1/+1 counters on each creature you control due to Doubling Season and Shang-Chi.
Activate Devoted Druid's first ability by tapping it, adding {G}.
Leyline of Abundance triggers, adding {G}.
Activate Devoted Druid's second ability by putting a -1/-1 counter on it, untapping Devoted Druid.
Repeat from step 2 three additional times.
Repeat from step 1.

Infinite +1/+1 counters on most creatures you control

Devoted Druid

Leyline of Abundance

Doubling Season

Activate Triskelion by removing a +1/+1 counter from it, dealing 1 damage to itself.
Rite of Passage triggers, putting two +1/+1 counters on Triskelion.
Repeat an arbitrarily large number of times.
Move to the next turn, removing all damage marked on Triskelion.
Activate Triskelion by removing a +1/+1 counter from it, dealing 1 damage to any target.
Repeat step 5 as desired.

Rite of Passage

Triskelion

Cast Strength of Will by paying {1}{G}, targeting Walking Ballista.
Activate Walking Ballista by removing a +1/+1 counter from it, dealing 1 damage to it.
Walking Ballista triggers, putting two +1/+1 counters on it due to Shang-Chi.
Activate Walking Ballista by removing a +1/+1 counter from it, dealing 1 damage to any target.
Repeat from step 2.

Infinite +1/+1 counters on a creature

Strength of Will

Activate Karn's Bastion by paying {4}, putting a charge counter on Lost Jitte and two +1/+1 counters on Cryptic Trilobite.
Activate Cryptic Trilobite's first ability twice by removing two +1/+1 counters from it, adding {C}{C}{C}{C} that can only be spent to activate abilities.
Activate Lost Jitte by removing a charge counter from it, untapping Karn's Bastion.
Repeat.

Infinite proliferate

Lost Jitte

Karn's Bastion

Cryptic Trilobite

Cast Gatta and Luzzu by paying {2}{W}.
When Gatta and Luzzu enters the battlefield, it triggers, targeting Triskelion.
Activate Triskelion by removing a +1/+1 counter from it, targeting itself, but instead putting two +1/+1 counters on it due to Gatta and Luzzu and Shang-Chi.
Activate Triskelion by removing a +1/+1 counter from it, dealing 1 damage to any target.
Repeat from step 3.

Gatta and Luzzu

Activate Pheres-Band Tromper by tapping it, adding {G}.
Activate Pheres-Band Tromper by paying {1} and putting a -1/-1 counter on it, untapping it.
Pheres-Band Tromper triggers, putting two +1/+1 counters on it.
Repeat.

Pheres-Band Tromper

Sinking Feeling

Citanul Hierophants

Play Power Depot, which will enter with a +1/+1 counter on it due to its modular ability
Cast Toph either from your hand or from the command zone by paying {2}{R}{G} plus commander tax if applicable.
When Toph enters, it triggers, earthbending Power Depot and putting a number of +1/+1 counters on Power Depot equal to the mana spent to cast Toph, increased by Shang-Chi.
Activate Altar of Dementia by sacrificing Power Depot.
When Power Depot dies, its modular ability and Toph trigger.
Resolve the modular trigger, putting the +1/+1 counters that were on Power Depot onto Crystalline Crawler, increased by Shang-Chi.
Resolve the Toph trigger, returning Power Depot from your graveyard to the battlefield tapped. Power Depot will enter with a +1/+1 counter on it due to its modular ability
Resolve the Altar of Dementia ability.
Activate Altar of Dementia by sacrificing Toph. Choose to return Toph from your graveyard to the command zone.
Activate Crystalline Crawler by removing a +1/+1 counter from it, adding {R/G}.
Repeat step 10 until you have enough mana to cast Toph.
Repeat from step 2.

Infinite ETB

Infinite LTB

Infinite colored mana

Infinite death triggers

Infinite landfall triggers

Infinite mill

Infinite sacrifice triggers

Infinite self-mill

Toph, Greatest Earthbender

Power Depot

Crystalline Crawler

Altar of Dementia

Activate Kenrith by paying {G}, putting two +1/+1 counters on Crystalline Crawler.
Activate Crystalline Crawler by removing a +1/+1 counter from it, adding {G}.
Repeat.

Infinite card draw for any number of players

Infinite draw triggers for any number of opponents

Infinite lifegain

Infinite lifegain triggers

Return all creature cards from all graveyards to the battlefield under your control

Kenrith, the Returned King

Zirda, the Dawnwaker

Combos with "Shang-Chi, Martial Mentor"