ΔE 13.4, fair: the same colour family, but not a straight swap. Warpfiend Grey is a little darker, more muted than Mauve.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Warpfiend Grey is a little darker, more muted than Mauve.
The same difference applies the other way round: Mauve is a little lighter, more saturated.
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 Mauve on the colour wheel See Warpfiend Grey on the colour wheel
All matches: Mauve equivalents · Warpfiend Grey equivalents