ΔE 20.1, loose: different enough that you should pick on purpose. Lustful Purple is noticeably lighter, more saturated than Warpfiend Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Lustful Purple is noticeably lighter, more saturated than Warpfiend Grey.
The same difference applies the other way round: Warpfiend Grey is noticeably darker, 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 Warpfiend Grey on the colour wheel See Lustful Purple on the colour wheel
All matches: Warpfiend Grey equivalents · Lustful Purple equivalents