How is Legowelt producing the main sound that you hear at 4:44 in this video? He lists the instruments he uses in this session at the beginning of the clip. He presses some buttons also to effect the sound, repeating a section of it at 4:51. The sound is reminiscent also of Boards of Canada.
I would try taking a saw or square wave, put on a 4 pole LPF filter with lots of resonance close to, or even into, self oscillation. Then either run the cutoff through a sample-and-hold LFO, or sequence it by hand.
Resample if you are running it through the LFO.
Then run it through a reverb unit. You probably want a medium-ish tail, with little to no pre delay, and attenuation on the high frequencies. Maybe 100% wet? Try it. If you do add some dry signal, you'll want to roll off the high end as well.
that should get you close.