Emerald Forest vs Goblinoid Green

How close are they?

ΔE 29.2, loose: different enough that you should pick on purpose. Goblinoid Green is a little lighter, much more muted than Emerald Forest.

Can I use Goblinoid Green instead of Emerald Forest?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Goblinoid Green is a little lighter, much more muted than Emerald Forest.

Can I use Emerald Forest instead of Goblinoid Green?

The same difference applies the other way round: Emerald Forest is a little darker, much 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.