Sim Modder is a cheat object which can be accessed by using testingcheatsenabled. It was first introduced in The Sims 2 Nightlife. It can be accessed by pressing "CTRL" "SHIFT" and "C" and typing boolprop testingcheatsenabled true. When holding "SHIFT" and clicking on one Sim, one of the options that should appear is "Spawn". When clicking on "Spawn", one of the options is "Sim Modder". This will not work if Nightlife isn't installed, but it will The Sims 2 Deluxe or The Sims 2 Double Deluxe is installed, as Nightlife is integrated into those games.

The Sim Modder appears as a baby standing up. Some of the things the Sim Modder can do are:

• Change the amount of skill points a Sim has
• Change a Sim's age
• Change a Sim's aspiration, including changing it to the hidden Power aspiration.
• Make/Cure vampires
• Change relationships with other Sims
• Increase/Decrease a Sim's aspiration points
• Add or remove want slots/locks
• Make Motives increase, decrease, or be in the middle for any Sim on the lot
• Change Personalities
• Change Aspirations
• Increase or Decrease Influence
• Switch Lifetime Aspirations

A player can use the Sim Modder to make vampires, but in some later expansions, using it to cure them will not work.