To finish up the mini-series on advanced masking, this video introduces the concept of "selection building". Though this is not an official title, it's a process by which you make the job of creating complex selections easier and less frustrating. This technique is especially useful if you're adding graphic or pattern overlays on to your characters. If this seems abstract or challenging make sure to give it a try for yourself -- like other types of masking, it's much easier once you've had a hands-on experience.
If you're not familiar with masking, these are good videos to watch first: Masking 101 pt.1, Masking 101 pt. 2, Masking 101 pt. 3
To follow along with the video, here's the robot PSD for download.
And to learn about applying 2D decals using the warp tool watch this video: Warp Tool