I think it’s a combination between doubled oscillators one octave apart and filter key-tracking. Try this:
Oscillator: Two of them, both medium pulse waves. Set the second oscillator up one octave, and give it a wide 3-voice unison with a fairly aggressive detune.
Filter: 24 dB lowpass. Turn down the cutoff and modulate it with an envelope to give it a quick decay/release, creating the “meow” sound. Turn up the resonance to really bring out the “meow”. Now turn on key-tracking, which will make higher notes brighter. Then disable the higher octave oscillator, and turn down the cutoff while playing a low note, until you hear some subby boom in it. Then turn the higher octave back on.
This will require a lot of tweaking of the various filter parameters. But the idea is, the low notes should trigger a cutoff value that creates a subby boomy sound, while the higher notes don’t.