Emerald Forest vs Troll Snot Green

How close are they?

ΔE 31.4, loose: different enough that you should pick on purpose. Troll Snot Green is noticeably lighter, much more muted than Emerald Forest.

Can I use Troll Snot Green instead of Emerald Forest?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Troll Snot Green is noticeably lighter, much more muted than Emerald Forest.

Can I use Emerald Forest instead of Troll Snot Green?

The same difference applies the other way round: Emerald Forest is noticeably 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.