ΔE 15.1, loose: different enough that you should pick on purpose. Violet is much more muted, cooler than Nightmare Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Violet is much more muted, cooler than Nightmare Purple.
The same difference applies the other way round: Nightmare Purple is much 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 Nightmare Purple on the colour wheel See Violet on the colour wheel
All matches: Nightmare Purple equivalents · Violet equivalents