Activate Necrotic Ooze using Devoted Druid's first ability by tapping it, adding {G}.
Activate Necrotic Ooze using Devoted Druid's second ability by putting a -1/-1 counter on it, untapping it.
Activate Necrotic Ooze using Grim Poppet's ability by removing a -1/-1 counter from it, targeting any other creature.
Holding priority, activate Necrotic Ooze using Devoted Druid's first ability by tapping it, adding {G}.
Repeat from step 2.

Infinite -1/-1 counters

Infinite green mana

Necrotic Ooze

Devoted Druid

Grim Poppet

Activate Phyrexian Altar by sacrificing Grim Poppet.
When Grim Poppet dies, its undying ability triggers, returning it from your graveyard to the battlefield without a +1/+1 counter on it due to its replacement effect.
Repeat.

Infinite colored mana

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Mikaeus, the Unhallowed

Phyrexian Altar

Activate Volrath by paying {1}, causing it to become a copy of Grim Poppet until your next turn.
Activate Grim Poppet by removing a -1/-1 counter from it, putting a -1/-1 counter on Volrath.
Hapatra triggers, creating a creature token.
Activate Volrath by removing a -1/-1 counter from it, putting a -1/-1 counter on Grim Poppet.
Hapatra triggers, creating a creature token.
Repeat from step 2.

Infinite creature tokens

Volrath, the Shapestealer

Hapatra, Vizier of Poisons

Activate Grim Poppet by removing a -1/-1 counter from it, putting a -1/-1 counter on Spark Double.
Hapatra triggers, creating a creature token.
Activate Spark Double by removing a -1/-1 counter from it, putting a -1/-1 counter on Grim Poppet.
Hapatra triggers, creating a creature token.
Repeat.

Spark Double

Activate Krark-Clan Ironworks by sacrificing Grim Poppet.
When Grim Poppet dies, its undying ability triggers, returning it from your graveyard to the battlefield without a +1/+1 counter on it due to its replacement effect.
Repeat.

Infinite colorless mana

Krark-Clan Ironworks

If Grim Poppet has any -1/-1 counters on it, activate it by removing a -1/-1 counter from it.
Repeat step 1 as necessary until Grim Poppet has no -1/-1 counters on it.
Activate Ashnod's Altar by sacrificing Grim Poppet.
When Grim Poppet dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Repeat.
Resolve all Grim Poppet abilities, putting infinite -1/-1 counters on any number of creatures.

Destroy each creature that enters the battlefield under an opponent's control

Destroy any number of creatures

Lock

Effects that Alter a Creature's Power/Toughness (Anthem Effects)

Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight

Ashnod's Altar

Activate Grim Poppet by removing a -1/-1 counter from it, targeting another creature.
Repeat until Grim Poppet has no -1/-1 counters on it.
Activate Antler Skulkin by paying {2}, giving Grim Poppet persist until end of turn.
Activate Krark-Clan Ironworks by sacrificing Grim Poppet, adding {C}{C}.
Grim Poppet dies, triggering its persist ability, returning it from your graveyard to the battlefield with a total of four -1/-1 counters on it.
Repeat.

Elesh Norn, Grand Cenobite

Painter's Servant

Antler Skulkin

Activate Grim Poppet by removing a -1/-1 counter from it, targeting another creature.
Repeat until Grim Poppet has no -1/-1 counters on it.
Activate Antler Skulkin by paying {2}, giving Grim Poppet persist until end of turn.
Activate Ashnod's Altar by sacrificing Grim Poppet, adding {C}{C}.
Grim Poppet dies, triggering its persist ability, returning it from your graveyard to the battlefield with a total of four -1/-1 counters on it.
Repeat.

Combos with "Grim Poppet"