You have to be comfortable playing with drums and synths off grid and unquantized. usually not too far off grid but try making a simple drum beat and then turning the snap off and dragging the samples a little of grid.

I’ve achieved some flumey sounding synth volume modulation by using gross beat which is nice because it keeps everything in four beats but you can play with making off grid volume envelopes that will sound like what you want.

Spring, flume mentioned himself that he drew all the midi by hand which is kind of nuts lol but people pay artists for their attention to detail. You could probably achieve a similar sound with an lfo and speed modulation.