How to Make Alien Sims in The Sims 2

Enter Create-a-Sim. Wait for it to load.

Enable testingcheats. Hold down Ctrl+⇧ Shift+C and type boolprop testingcheatsenabled true. Press ↵ Enter to enable the cheat.

Press ⇧ Shift+N. This will enable debugging mode in Create-a-Sim and give you access to genetics and outfits that aren't typically available, enabling you to create aliens.

Create a new Sim. The Sim can be any age or gender.

Choose the alien skin from the custom skin bin. Click on the star icon next to the four skin tones; a box will pop up with other available skin tones. Find the plain green square and click on it to give your Sim the alien skintone. You'll also see some other hidden skintones, like the Body Shop mannequin skintone.

Give your Sim black eyes. Click on tab 3 to edit your Sim's hair and face, and go to the Eyes tab. Debug Mode will have enabled the pitch-black alien eyes.

Adjust their facial structure. The default Pollination Technician NPC, as well as Pollination Technician #9 Smith from Strangetown and Pollination Technician #7 in the Caliente family tree, have very exaggerated facial features. You can make your alien Sims have wild facial structures, or you can choose to make them look like typical Sims. If you want to create really wild facial structures, open the tab of a random facial feature (for instance, the mouth). Drag at least one slider all the way over to the left or the right. Go to another tab (e.g. eyes), click on one of the preset options at the top of the window, and then return to the tab of the first feature you edited. The slider should have reset itself, meaning you can continue editing the feature to an outrageous extent.

Edit their other features as you like. Aside from their skin tone and eye color, alien Sims are essentially just like non-alien Sims, so you can give them whatever name, clothes, aspiration, and personality you want. Once you're finished making alien Sims, you can turn off debugging mode by pressing ⇧ Shift+M and then disable testingcheats with boolprop testingcheatsenabled false.

Confirm the Sim and create the household. Once you've finished creating your Sim, click on the checkbox to confirm them. From there, you can create further Sims, set family ties, or simply create the household by clicking the checkbox. Your alien Sims are now ready to be moved into a lot!