ΔE 23.2, loose: different enough that you should pick on purpose. Plasma Red is noticeably lighter, much more saturated than Demon Brown.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Plasma Red is noticeably lighter, much more saturated than Demon Brown.
The same difference applies the other way round: Demon Brown is noticeably darker, much more muted.
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 Demon Brown on the colour wheel See Plasma Red on the colour wheel
All matches: Demon Brown equivalents · Plasma Red equivalents