Moodlets can be triggered by specific events, proximity to certain areas or objects, or by very low or very high motives. Moodlets can have a positive, negative, or neutral affect on a Sim's mood. Sim needs are also updated, with much of the functionality of these needs replaced or augmented by moodlets. These traits influence a Sim's behavior and wishes, including their lifetime wish.

The Sims 3 replaces the points-based personality system of The Sims and The Sims 2 with a system based on unique traits. The Sims 3 also introduces the Create a Style tool to the series, which allows players to change the patterns and colors of objects and clothing, and copy styles between different objects.

The Sims 3 features robust customization options through an expanded build mode and Create a Sim.

The Sims 3 is the first game to feature an open-world concept: players are no longer limited to having a single lot loaded at a time, and Sims are able to move about and explore an entire town without triggering a loading screen. The Sims 3 keeps many of the innovations introduced by its predecessor, but adds several new features. Like other The Sims games, The Sims 3 focuses on creating and controlling virtual worlds filled with simulated people called ' Sims.' The Sims 3 is the third main title in The Sims series of video games.

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