There’s quite a bit that ‘sidechain’ covers nowadays that it’s almost a shame to umbrella it all under that term.
Like there’s the stadium compression -remove anything in it’s way huge (slightly primitive sometimes) sounding one, where it’s almost like a limiter.
And then there’s a more sculpting one, where you go for a more frequency dependant sort of approach. Like some complex buss grouped thing - or really carefully set up the threshold in relation to each layer you want sidechained and then resample the effect and render it back as tracks of audio.
Yeah not sure which one, defo not 808,909,707,606,626…i’ve heard it in another song but can’t for the life of me remember which one - exactly the same sound as in the track you posted. It might even be from a synth and not a drum machine
Could get fairly close by layering a square with a sinewave, the sine an octave below. Perhaps some stereo detune on the square + LP filter automation for the opening and closing.
You mean the “yah” sound?
Take a saw/square with an LP filter, with low cutoff knob, and high resonance knob. Play with an LFO or envelope on the cutoff, add some flangers/chorus, and most importantly of all, bitcrushing. There’s tons of free bitcrush distortion effects on the web. One of the best ones, imo, is “Geektronic”.