ΔE 28.5, loose: different enough that you should pick on purpose. Belladonna Green is a little darker, more saturated, cooler than Rigor Mortis.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Belladonna Green is a little darker, more saturated, cooler than Rigor Mortis.
The same difference applies the other way round: Rigor Mortis is a little 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 Rigor Mortis on the colour wheel See Belladonna Green on the colour wheel
All matches: Rigor Mortis equivalents · Belladonna Green equivalents