This is how I got this chevo;
1. I found one of the seven Ink locations just north east of Croakwood. You can get there just going all the way north east and eventually you will end up a hay field. Of course kill all enemies along the way.
2. There you will find a "ominous scarecrow"
3. Just interact this thing and you will be teleported straight to a boss battle so be prepared before this !
Chevo will unlock after you have interacted the scarecrow !