You control at least one other nontoken creature.
Enduring Bondwarden has at least one coin counter on it.

Activate Viscera Seer by sacrificing Enduring Bondwarden.
When Enduring Bondwarden dies, it and Athreos' third ability trigger.
Resolve the Enduring Bondwarden trigger, putting all counters from it onto another nontoken creature you control.
Resolve the Athreos trigger, returning Enduring Bondwarden from your graveyard to the battlefield.
When Enduring Bondwarden enters the battlefield, its backup ability triggers, putting a +1/+1 counter on the creature who had a coin counter placed on it, and giving it the printed ability until end of turn.
Resolve the Viscera Seer ability from step 1, causing you to scry 1.
Activate Viscera Seer by sacrificing the nontoken creature with a coin counter on it.
When the creature dies, it and Athreos' third ability trigger.
Resolve the creature's trigger, putting all counters from it onto Enduring Bondwarden .
Resolve the Athreos trigger, returning the creature from your graveyard to the battlefield.
Resolve the Viscera Seer ability from step 7, causing you to scry 1.
Repeat.

You control at least one other nontoken creature.
Enduring Bondwarden has at least one coin counter on it.

Activate Ashnod's Altar by sacrificing Enduring Bondwarden, adding .
When Enduring Bondwarden dies, it and Athreos' third ability trigger.
Resolve the Enduring Bondwarden trigger, putting all counters from it onto another nontoken creature you control.
Resolve the Athreos trigger, returning Enduring Bondwarden from your graveyard to the battlefield.
When Enduring Bondwarden enters the battlefield, its backup ability triggers, putting a +1/+1 counter on the creature who had a coin counter placed on it, and giving it the printed ability until end of turn.
Activate Ashnod's Altar by sacrificing the nontoken creature with a coin counter on it, adding .
When the creature dies, it and Athreos' third ability trigger.
Resolve the creature's trigger, putting all counters from it onto Enduring Bondwarden .
Resolve the Athreos trigger, returning the creature from your graveyard to the battlefield.
Repeat.

You control at least one other nontoken creature.
Enduring Bondwarden has at least one coin counter on it.

Activate Carrion Feeder by sacrificing Enduring Bondwarden.
When Enduring Bondwarden dies, it and Athreos' third ability trigger.
Resolve the Enduring Bondwarden trigger, putting all counters from it onto another nontoken creature you control.
Resolve the Athreos trigger, returning Enduring Bondwarden from your graveyard to the battlefield.
When Enduring Bondwarden enters the battlefield, its backup ability triggers, putting a +1/+1 counter on the creature who had a coin counter placed on it, and giving it the printed ability until end of turn.
Resolve the Carrion Feeder ability from step 1, putting a +1/+1 counter on it.
Activate Carrion Feeder by sacrificing the nontoken creature with a coin counter on it.
When the creature dies, it and Athreos' third ability trigger.
Resolve the creature's trigger, putting all counters from it onto Enduring Bondwarden .
Resolve the Athreos trigger, returning the creature from your graveyard to the battlefield.
Resolve the Carrion Feeder ability from step 7, putting a +1/+1 counter on it.
Repeat.

You control at least one other nontoken creature.
Enduring Bondwarden has at least one coin counter on it.

Activate Phyrexian Altar by sacrificing Enduring Bondwarden, adding one mana of any color.
When Enduring Bondwarden dies, it and Athreos' third ability trigger.
Resolve the Enduring Bondwarden trigger, putting all counters from it onto another nontoken creature you control.
Resolve the Athreos trigger, returning Enduring Bondwarden from your graveyard to the battlefield.
When Enduring Bondwarden enters the battlefield, its backup ability triggers, putting a +1/+1 counter on the creature who had a coin counter placed on it, and giving it the printed ability until end of turn.
Activate Phyrexian Altar by sacrificing the nontoken creature with a coin counter on it, adding one mana of any color.
When the creature dies, it and Athreos' third ability trigger.
Resolve the creature's trigger, putting all counters from it onto Enduring Bondwarden .
Resolve the Athreos trigger, returning the creature from your graveyard to the battlefield.
Repeat.

You control at least one other nontoken creature.
Enduring Bondwarden has at least one coin counter on it.

Activate Altar of Dementia by sacrificing Enduring Bondwarden.
When Enduring Bondwarden dies, it and Athreos' third ability trigger.
Resolve the Enduring Bondwarden trigger, putting all counters from it onto another nontoken creature you control.
Resolve the Athreos trigger, returning Enduring Bondwarden from your graveyard to the battlefield.
When Enduring Bondwarden enters the battlefield, its backup ability triggers, putting a +1/+1 counter on the creature who had a coin counter placed on it, and giving it the printed ability until end of turn.
Resolve the Altar of Dementia ability from step 1, causing target player to mill cards equal to Enduring Bondwarden's power.
Activate Altar of Dementia by sacrificing the nontoken creature with a coin counter on it.
When the creature dies, it and Athreos' third ability trigger.
Resolve the creature's trigger, putting all counters from it onto Enduring Bondwarden .
Resolve the Athreos trigger, returning the creature from your graveyard to the battlefield.
Resolve the Altar of Dementia ability from step 7, causing target player to mill cards equal to the sacrificed creature's power.
Repeat.