ΔE 25.2, loose: different enough that you should pick on purpose. Nurgling Green is noticeably lighter, warmer than Forest of Shadows.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Nurgling Green is noticeably lighter, warmer than Forest of Shadows.
The same difference applies the other way round: Forest of Shadows is noticeably darker, 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 Forest of Shadows on the colour wheel See Nurgling Green on the colour wheel
All matches: Forest of Shadows equivalents · Nurgling Green equivalents