ΔE 15.6, loose: different enough that you should pick on purpose. Berserker Red is noticeably darker, more muted, cooler than Mournfang Brown.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Berserker Red is noticeably darker, more muted, cooler than Mournfang Brown.
The same difference applies the other way round: Mournfang Brown is noticeably lighter, more saturated, 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 Mournfang Brown on the colour wheel See Berserker Red on the colour wheel
All matches: Mournfang Brown equivalents · Berserker Red equivalents