At the beginning of your upkeep, Second Chance triggers, causing you to sacrifice it and take an extra turn after this one.
Deal combat damage to an opponent using Harnessed Snubhorn.
Harnessed Snubhorn triggers, returning Second Chance from your graveyard to the battlefield.
Repeat each turn.

Infinite turns

Lock

Harnessed Snubhorn

Second Chance

Deal combat damage with Harnessed Snubhorn.
Harnessed Snubhorn triggers, returning Myr Battlesphere from your graveyard to the battlefield.
Myr Battlesphere enters the battlefield, creating four 1/1 Myr creature tokens.
Activate Time Sieve by tapping it, sacrificing Myr Battlesphere and sacrificing the four Myr tokens, causing you to take an extra turn after this one.
Repeat each turn.

Time Sieve

Myr Battlesphere

Deal combat damage to an opponent using Harnessed Snubhorn, triggering it and Breath of Fury.
Resolve the Harnessed Snubhorn trigger, returning Copy Artifact from your graveyard to the battlefield as a copy of Harnessed Snubhorn.
Resolve the Breath of Fury trigger, causing you to sacrifice Harnessed Snubhorn, then attach Breath of Fury to Copy Artifact, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Deal combat damage to an opponent using Copy Artifact, triggering it and Breath of Fury.
Resolve the Copy Artifact trigger, returning Harnessed Snubhorn from your graveyard to the battlefield.
Resolve the Breath of Fury trigger, causing you to sacrifice Copy Artifact, then attach Breath of Fury to Harnessed Snubhorn, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Repeat.

Infinite combat damage

Infinite combat phases

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite mana creatures you control can produce

Infinite creature sacrifice triggers

Infinite untap of creatures you control

Breath of Fury

Encroaching Mycosynth

Copy Artifact

Urabrask the Hidden

Deal combat damage to an opponent using Harnessed Snubhorn, triggering it and Breath of Fury.
Resolve the Harnessed Snubhorn trigger, returning Sculpting Steel from your graveyard to the battlefield as a copy of Harnessed Snubhorn.
Resolve the Breath of Fury trigger, causing you to sacrifice Harnessed Snubhorn, then attach Breath of Fury to Sculpting Steel, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Deal combat damage to an opponent using Sculpting Steel, triggering it and Breath of Fury.
Resolve the Sculpting Steel trigger, returning Harnessed Snubhorn from your graveyard to the battlefield.
Resolve the Breath of Fury trigger, causing you to sacrifice Sculpting Steel, then attach Breath of Fury to Harnessed Snubhorn, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Repeat.

Sculpting Steel

Deal combat damage to an opponent using Harnessed Snubhorn, triggering it and Breath of Fury.
Resolve the Harnessed Snubhorn trigger, returning Mirrormade from your graveyard to the battlefield as a copy of Harnessed Snubhorn.
Resolve the Breath of Fury trigger, causing you to sacrifice Harnessed Snubhorn, then attach Breath of Fury to Mirrormade, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Deal combat damage to an opponent using Mirrormade, triggering it and Breath of Fury.
Resolve the Mirrormade trigger, returning Harnessed Snubhorn from your graveyard to the battlefield.
Resolve the Breath of Fury trigger, causing you to sacrifice Mirrormade, then attach Breath of Fury to Harnessed Snubhorn, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Repeat.

Mirrormade

Deal combat damage to an opponent using Harnessed Snubhorn, triggering it and Breath of Fury.
Resolve the Harnessed Snubhorn trigger, returning Hulking Metamorph from your graveyard to the battlefield as a copy of Harnessed Snubhorn.
Resolve the Breath of Fury trigger, causing you to sacrifice Harnessed Snubhorn, then attach Breath of Fury to Hulking Metamorph, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Deal combat damage to an opponent using Hulking Metamorph, triggering it and Breath of Fury.
Resolve the Hulking Metamorph trigger, returning Harnessed Snubhorn from your graveyard to the battlefield.
Resolve the Breath of Fury trigger, causing you to sacrifice Hulking Metamorph, then attach Breath of Fury to Harnessed Snubhorn, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Repeat.

Hulking Metamorph

Deal combat damage to an opponent using Harnessed Snubhorn, triggering it and Breath of Fury.
Resolve the Harnessed Snubhorn trigger, returning Phyrexian Metamorph from your graveyard to the battlefield as a copy of Harnessed Snubhorn.
Resolve the Breath of Fury trigger, causing you to sacrifice Harnessed Snubhorn, then attach Breath of Fury to Phyrexian Metamorph, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Deal combat damage to an opponent using Phyrexian Metamorph, triggering it and Breath of Fury.
Resolve the Phyrexian Metamorph trigger, returning Harnessed Snubhorn from your graveyard to the battlefield.
Resolve the Breath of Fury trigger, causing you to sacrifice Phyrexian Metamorph, then attach Breath of Fury to Harnessed Snubhorn, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Move to your next combat phase.
Repeat.

Combos with "Harnessed Snubhorn"