Ok, it's some basic stuff which actually shows what sequencers were invented for ;) but it's quite catchy and most probably people, interested in finding the answer to: how to make Deadmau5 style chords / plucks, will like it. It just shows how to start from a single note and build the chords around it.
So if you think that chords are made by hand ... you're wrong ;) Today it's about using a sequencer and mouse clicking ;)
Do you like it ? I don't - mouse clicking is so uninspiring :) Still prefer to just record the chords played by hand + quantization and then if needed add some lower layer, or just use Ableton Chord Midi Effect (neat effect which quickly build chords so for example you can hear your preset playing at current octave and -1 octave lower without creating another instance of your synth transposed -12 semi-tones).