The base is original from the producer (chords and melodies), but is complemented with elements that complement the song that come from samplepacks, usually, vocal chops, guitars, wobbles sections, glitch effects. It is the standard in which most of producers work, in a project you will find MIDI files made by the producer, but also melodic loops.
The bass is made up from a synth and a percussion layer, the leads are various layers made with serum and ableton's operator. There is one 'melodic loop sample' which i wouldn't consider melodic loop sample because its just an ambient pad in the background layered to the unrecognisable.
Sample pack Splice fantasy world
Loop name ESM 6 unexplored cave