ΔE 19.3, loose: different enough that you should pick on purpose. Stormfiend is noticeably lighter, much more saturated, cooler than Occultist Cloak.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Stormfiend is noticeably lighter, much more saturated, cooler than Occultist Cloak.
The same difference applies the other way round: Occultist Cloak is noticeably darker, much more muted, warmer.
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 Stormfiend on the colour wheel
All matches: Occultist Cloak equivalents · Stormfiend equivalents