At the beginning of your precombat main phase, There and Back Again and City of Death trigger.
Resolve the There and Back Again trigger, putting a lore counter on it.
There and Back Again's third chapter ability and Sigurd trigger.
Resolve the Sigurd trigger, putting a +1/+1 counter on a creature you control.
Resolve the There and Back Again trigger, creating a legendary 6/6 Smaug creature token and causing you to sacrifice There and Back Again.
Resolve the City of Death trigger, putting a lore counter on it.
City of Death's second chapter ability and Sigurd trigger.
Resolve the Sigurd trigger, putting a +1/+1 counter on a creature you control.
Resolve the City of Death trigger, creating a copy of the Smaug token.
Put a Smaug token into your graveyard due to the legend rule.
When the Smaug token dies, it triggers, creating fourteen Treasure tokens.
Declare Sigurd as an attacker.
Activate a Treasure by tapping and sacrificing it, adding {1}.
Activate Sigurd by paying {1}, removing a lore counter from City of Death.
Activate Time Sieve by tapping it and sacrificing five Treasures, causing you to take an extra turn after this one.
Move to your next turn.
At the beginning of your precombat main phase, City of Death triggers, putting a lore counter on it.
Repeat from step 7.

Infinite turns

Sigurd, Jarl of Ravensthorpe

Time Sieve

There and Back Again

City of Death

At the beginning of your precombat main phase, There and Back Again and Three Blind Mice trigger.
Resolve the There and Back Again trigger, putting a lore counter on it.
There and Back Again's third chapter ability and Sigurd trigger.
Resolve the Sigurd trigger, putting a +1/+1 counter on a creature you control.
Resolve the There and Back Again trigger, creating a legendary 6/6 Smaug creature token and causing you to sacrifice There and Back Again.
Resolve the Three Blind Mice trigger, putting a lore counter on it.
Three Blind Mice's second chapter ability and Sigurd trigger.
Resolve the Sigurd trigger, putting a +1/+1 counter on a creature you control.
Resolve the Three Blind Mice trigger, creating a copy of the Smaug token.
Put a Smaug token into your graveyard due to the legend rule.
When the Smaug token dies, it triggers, creating fourteen Treasure tokens.
Declare Sigurd as an attacker.
Activate a Treasure by tapping and sacrificing it, adding {1}.
Activate Sigurd by paying {1}, removing a lore counter from Three Blind Mice.
Activate Time Sieve by tapping it and sacrificing five Treasures, causing you to take an extra turn after this one.
Move to your next turn.
At the beginning of your precombat main phase, Three Blind Mice triggers, putting a lore counter on it.
Repeat from step 7.

Combos with "Sigurd, Jarl of Ravensthorpe"