Mythical Orange vs Trollslayer Orange

How close are they?

ΔE 8.8, close: similar, with a visible difference side by side. Trollslayer Orange is a little lighter, more muted than Mythical Orange.

Can I use Trollslayer Orange instead of Mythical Orange?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Trollslayer Orange is a little lighter, more muted than Mythical Orange.

Can I use Mythical Orange instead of Trollslayer Orange?

The same difference applies the other way round: Mythical Orange is a little darker, 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.