ΔE 16.0, loose: different enough that you should pick on purpose. Flat Green is noticeably darker, more saturated, cooler than Bestial Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Flat Green is noticeably darker, more saturated, cooler than Bestial Green.
The same difference applies the other way round: Bestial Green is noticeably lighter, 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 Bestial Green on the colour wheel See Flat Green on the colour wheel
All matches: Bestial Green equivalents · Flat Green equivalents