How does a Stage II Coastal Lands card interact with the Fortification event *(After advancing Invader Cards: Invaders Build in one terrain not shown under any Invader Action)*?
How does a Stage II Coastal Lands card interact with the Fortification event (After advancing Invader Cards: Invaders Build in one terrain not shown under any Invader Action)?
It doesn't -- it is treated as though the card were blank.
"Coastal Lands" is not a terrain type.