ΔE 16.3, loose: different enough that you should pick on purpose. Undead Dragon is a little lighter, more muted, warmer than Briar Queen Chill.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Undead Dragon is a little lighter, more muted, warmer than Briar Queen Chill.
The same difference applies the other way round: Briar Queen Chill is a little darker, more saturated, cooler.
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 Briar Queen Chill on the colour wheel See Undead Dragon on the colour wheel
All matches: Briar Queen Chill equivalents · Undead Dragon equivalents