Or better said, the people using Photoshop would never cease to amaze me.
The thing I like most is the way he paints in greyscale and then modifies colours using the Hue & Saturation panel. The use of the Liquify tool to adjust the volumes is really smart too -- and quite effective.
Note: before playing, turn off your volume and play some other music. Trust me, you don't want to destroy the bliss of watching this time lapse with the video's soundtrack. [Buzzfeed]