infinite turns (easy to pull off) and once the city is out, there is nothing an opponent can do :)

Players can cast spells and activate abilities only during their own turns.

Exile Time Spiral. Each player shuffles their hand and graveyard into their library, then draws seven cards. You untap up to six lands.

Imprint — , : You may exile an instant or sorcery card with mana value X from your hand. At the beginning of your upkeep, you may copy a card exiled with this artifact. If you do, you may cast the copy without paying its mana cost.