ΔE 22.2, loose: different enough that you should pick on purpose. Nightshade Purple is a little darker, much more saturated, warmer than Occultist Cloak.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Nightshade Purple is a little darker, much more saturated, warmer than Occultist Cloak.
The same difference applies the other way round: Occultist Cloak is a little lighter, much more muted, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Occultist Cloak on the colour wheel See Nightshade Purple on the colour wheel
All matches: Occultist Cloak equivalents · Nightshade Purple equivalents