I dunno

You'll get a letter after saving wizard from Grim mountains.

Nothing at all till now. Maybe they add something interesting in the dark Forest in upcoming updates

You need to save the wizard from grim mountains, then you'll get the letter

Yep they help you afterwards in the story

You simply can't enter the ghost Portal. The portal is sort of dying or something...

Move forward and run at the same tym. It'll take some tries but it works.

Transform into cat and walk on the wooden planks laid there, pass the cat tunnel and cross the planks again.

The haunted house statue on ground floor