How to add some shade to a scene in After Effects

Hello,  

I want to add some shade to an actor's arm.

Is there an effect or ?  to simply add shade to a certain area... 

I know I could add a 2nd layer, and cut a mask in the top layer, and feather it out, but,

I have a bunch to do, and was wondering if there is an easier way.

I wish spotlight would project darkness also.  I tried changing spotlight's color to black, but didn't work.

Thanks,

Letty