ΔE 17.9, loose: different enough that you should pick on purpose. Bright Brass (Met.) is noticeably lighter, more saturated than Mythril Blade.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Bright Brass (Met.) is noticeably lighter, more saturated than Mythril Blade.
The same difference applies the other way round: Mythril Blade 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 Mythril Blade on the colour wheel See Bright Brass (Met.) on the colour wheel
All matches: Mythril Blade equivalents · Bright Brass (Met.) equivalents