I think there's a bug in the game...I have went to the spooky forest for so many times and I never once recieved material for black dye , neither am I able to befriend any of the monsters there .
In order to get black grass you need to befriend Skippy in the spooky forest when u find him use last fighting option so keep doing it till u get a cutscene
It's a rare gift so u need to check every day he only gives 1 item per day I got mine pretty quickly within 3 days hope that helps
