Yes you can, if you’ve changed it enough. You can’t just take the default mannequin and use it as the main character for your game, although, if you use the mannequin as the basis and give it hair, clothing, armour etc, then that’s fine. As long as it’s not IMMEDIATELY recognisable as the Adjustable Mannequin, then you can use it.

The Adjustable Mannequin uses a Rig to pose the character and move the sliders. A Rig is a special type of object in Blender that allows us to animate and move bones. Make sure you enter Pose Mode in the top left corner of the screen.

The Presets were created using Blender’s Asset Library, and this needs to be enabled in the Preferences, you can find the explanation here. In the future this may be enabled by default, but for now you have to enable it in the Preferences.

The Adjustable Mannequin is only compatible with the newest version of Blender (or some older versions, check the compatibility section). If you open it in an older version of Blender, Blender will crash. So if you double click the Adjustable Mannequin file and Blender immediately crashes, it’s because you are using an incompatible version of Blender.