mixing.
Another nice chiptuney song. As for the "full" feel, you need proper mixing of the instruments to ensure their frequencies do not clash. Assign eash instrument to a mixer channel and then load a parametric EQ so they occupy their own part of the frequency spectrum. Yea.
Now that I think about it, Chiptune does not really too much mixing as the sounds are so lofi. The most mixing would be done on the kick if anything.