City of Jade

Whenever you cast an instant or sorcery spell, you may put a jewel counter on City of Jade.
If there are five or more jewel counters on it, for the rest of the game, islands you control add {u}{u} to your mana pool.
If there are ten or more jewel counters on it, for the rest of the game, instants and sorcery spells you cast can't be countered.