ΔE 30.0, loose: different enough that you should pick on purpose. Undead Dragon is a little lighter, much more muted, warmer than Thunderbird Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Undead Dragon is a little lighter, much more muted, warmer than Thunderbird Blue.
The same difference applies the other way round: Thunderbird Blue is a little darker, much 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 Thunderbird Blue on the colour wheel See Undead Dragon on the colour wheel
All matches: Thunderbird Blue equivalents · Undead Dragon equivalents