The Sims 2 DS Cheats

Mongoo Monkey:

Have a Sims 2 Game Boy Advance game in the cartridge slot to unlock Mongoo Monkey in the Casino.

More aliens:

Want to fight more aliens? Set your system clock ahead one minute. Load your game and walk around for a minute, then set the system clock back to normal time. The bellhop should tell you you're a time traveler, and the aliens have launched a full scale attack. Make sure to touch the clock as soon as it appears, or you'll lose all your sanity.

Alien Autopsy:

First, go to the desert with a metal detector. Find the crashed spaceship and use the detector there to get a mummified alien. Now, buy the Government Lab for 2,000 simoleons. Get near to the table and select 'alien autopsy'.

Thanks to Revolution Reader gavin and buki!