What is a Twin City
You may establish Friend, Foe, or Twin City relationships with your in-game neighbors. A Twin City relationship may be established only with a neighbor with a "Friend" or higher relationship, so a Foe relationship cannot become a Twin City relationship without being restored to a Friend one. A Twin City relationship is designated by a bright blue border around your neighbor's picture.
Why Have a Twin City
Some quests require you to perform actions in a Twin City, or to send gifts to your Twin City.
The rare collectible Unity is available only as a result of performing Twin City actions. Unity can be obtained from your Twin City, but can also be obtained by performing Twin City actions in Friend cities. Twin City actions cannot be performed in Foe cities.
How To Get a Twin City
Each Friend action and Twin City action you perform in a neighboring city moves the progress bar to the right, and each Foe action moves the progress bar to the left. When the bar is filled, you advance to the next Friend or Twin relationship, and when the bar is emptied, you advance to the next Foe relationship.
Twin City actions are unlocked when you reach the third Friend relationship, "Friends". Perform three Twin City actions during a single visit to send a Twin City invitation.
You may only have one Twin City relationship. If you send a Twin City invite to somebody who already has a Twin City, you will send a "break-up request," asking them to end their existing Twin City relationship and establish one with you.
When you establish a Twin City relationship, you begin with a brand new relationship (no collectible drop bonuses). If you later terminate your Twin City relationship, you will return to the Friend relationship you had before. However, if you or your Twin terminate your Twin City relationship and then re-establish it, you will return to a brand new twin city relationship level. See Relationships for the Twin City relationship levels, gifts, and collectible drop probabilities.
Twin City Gifts
Balloon Celebration - Available upon becoming a Twin City
The You're Awesome Flying Circus - Available upon the second relationship upgrade, "Connected"
Fighter Plane Flyover - Available upon the fourth relationship upgrade, "Associates"