The original liqueur formulated by Brother Antoine from the 'elixir' (Chartreuse Elixir Végétal). Green Chartreuse is flavoured with extracts from 132...
I tried Ver as a substitute. It was decent in the Last Word and a few other cocktails I tried. More Anise in Ver, which I really don't care for. In the meantime I will keep searching for Chartreuse.