Bad Birds/guide

Bird Mask
(Book Effect is required).

Go down the top-right ladder of the Nexus. Use the Book effect to open the large book to the right of the entrance. Go right over the book, take the first path down and interact with the crack in the wall between the two open books. From where you're teleported, go north-east and find an area with piles of bird skulls. Interact with the tall wolf/dog character holding a mask.

Broken
Go down the top-left ladder in the Nexus. Go up until you hit a wall. Go behind the wall and follow the wall as it goes to the left. Interact with the flashing painting.

Skeleton
Go down the bottom-left ladder in the Nexus. Go left and collect the skull beside the river. Go right and collect the pelvic and leg bone near the blue car. Go to the top-right corner of the world and collect the ribcage at the end of a winding path.

Once you collect all three bones, go towards the top-left corner of the world where a large body of water is. Bring the bones to the large bird in the water and you'll be given the effect.

Book
Go down the top-right ladder of the Nexus. Navigate your way through the maze to a room on the right side of the area full of bookshelves. Interact with the open book sitting on one of the bookshelves.

Panpipe
Go down the bottom-left ladder of the Nexus. Go right and interact with the car with broken windows. You'll be brought to a beach area. Go right and step over the shinging object on the ground.