I'd like to achieve something similar to that descending pitch heavy sound as heard here : https://clyp.it/jf0uqdoq# Any idea?
Use a SINE wave signal (yes read on)
Let it dive an octave (either by gradual resampling, generator pitch automation or LFO / Wheel pitch control on your synth)
Add a percussive hit to the start (like a kick drum)
Feed that into a distortion/overdrive/clipper (consider a guitar amp simulator).
The overdrive/distortion will transform the sine wave form towards a square wave as the signal tops are clipped away.
This overdrive step is quite crucial to the way the initial hit also influences the distortion of the sine. A square might work out too, but I don't think that is what is going on here. It sounds much like a subkick bass dive sample distorted heavily and these are mostly made of diving sines with a kick/floortom sample in the start.