ΔE 30.1, loose: different enough that you should pick on purpose. Plague Brown is more saturated, cooler than Pyrrhic Dawn.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Plague Brown is more saturated, cooler than Pyrrhic Dawn.
The same difference applies the other way round: Pyrrhic Dawn is 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 Pyrrhic Dawn on the colour wheel See Plague Brown on the colour wheel
All matches: Pyrrhic Dawn equivalents · Plague Brown equivalents