I think the main character of this sound comes from a combination of Distortion and Oscillator Sync. Here’s the main parts of what I did:
Osc: Saw. Use Oscillator Sync to get that grindy sound out of it. Experiment with the semi setting to get the right pitch.
Filter: Low Pass. 24 dB. Take it down quite a bit. We’ll be adding highs back in with…
Distortion: Use a warm Distortion style and don’t be afraid to really crank it on the nastier notes.
The varying timbre of the notes doesn’t seem to be modulated by an LFO, so my guess is that this track uses a Mod Wheel to modulate Distortion amount. This way some notes sound grungier and warmer, and some sound nastier.