I have a simple character rig, and I want my Mouse Look actuator to work with my a bone in my character rig, not my object. How can I achieve this? I want my character head to look up when my mouse does. (Left and right does not matter)
Simply add the mouselook to the armature instead. After doing this, you will realize that the ENTIRE rig points to the center of the screen. Quite obviously, this would be undesirable.
To fix, go into edit mode, select the top half of the armature, and hit Ctrl+Alt+P. Then Tab out of edit-mode and Parent>Bone the top armature to the top bone in the lower armature. see this answer to do that if you can't figure it out.
Remove the mouselook from the bottom armature, or add it just too the top if you don't have it yet.