Please correct me if I'm wrong, but the oscillator only produces one waveform (can't remember if this is a saw or triangle) - this is split into three more signals which take the 'native' waveform and transform into the target waveform with some circuitry. These are then sent to the mixer which you control using the waveform sliders. Some of the waveforms have further processing available like the ultra saw and the metalizer. Hope that helps!

It's probably mostly like that. Some base waveform oscillator, that is fed through waveshaping circuits.

It just depends on what the base waveform is.

I think I've seen somewhere that the base oscillator is a sawtooth. So the sawtooth is fed into the ultrasaw delay/phaseshifting circuit. But it also goes to the square wave shaper, which is a very simple circuit that uses a comparator to compare the current voltage of the sawtooth to some threshold (turning on only when it's above the threshold). Adjusting this threshold gives you PWM.

Then there's the triangle, which I don't know exactly how it does it, but it takes the sawtooth and turns it into a triangle, then runs it thru the wavefolder circuit of the metalizer.

Then there's the suboscillator, which (again, I'm not sure how) just divides the frequency by 2. Perhaps there's a circuit that takes the pulses from the squarewave and divides it by 2 or 4 (-1 or -2 octave). This can be easily done with a circuit that toggles on and off every cycle of the squarewave. (two of those in a row for the -2 octave). Then my guess is that the resulting octave(s)-down squarewave is shaped into a sine wave. That could explain the little blip in the sine wave, meaning it's not a perfect waveshaper (I'd imagine it's not trivial removing all the overtones of a squarewave).

my thoughts.

Never really thought about this before. But it's kinda fun to ponder on it.