Nijuu Yuumu (二重遊夢)/guide

Wings
Enter the white door in the Nexus. Go north until you see a feather to your right. Interact with the feather to get the effect.

Reaper
Enter the bluish-grey door in the Nexus. Go south until you can't see the bloodstain, then go right until you see the Reaper. Interact with him to get the effect.

Pencil
Enter the door in the Nexus that doesn't look like a door, then choose the brownish door. Go north-east and pass between two upright pencils--one orange, the other blue. In the next room, interact with the blue and orange pencils to get the effect.

Sprout
Enter the green door in the Nexus. Go north-east until you reach a gray house. Once inside, interact with the green-haired NPC to get the effect.

Orange
Enter the green door in the Nexus. Go north-east until you reach a gray house. Once inside, interact with the carrot. Then head south and interact with the orange to get the effect.

Headless
Enter the green door in the Nexus. Go north-west and interact with the crossing green lines. Make your way through dark maze and interact with the headless NPC. In the next area, go north-west and interact with the headless wandering NPCs to get the effect.

Negative
Enter the bluish-grey door in the Nexus. Go south-east until you find a geometric floating NPC. Interact with it to be teleported to Wasabi Hell. Navigate the maze until the pace opens up into an area with a hand figure at the top. (You know you're headed in the right direction when you have to lure a chaser out that's blocking the way.) Interact with the hand, then head north and interact with the tricolor lump (the one at the top) to get the effect.

Jar
Enter the door in the Nexus that doesn't look like a door, then choose the dark blue door. Go west until you can't, then go north. Then proceed east, and take the path above the path you just took; this path leads west. Follow the path, and then take the left north path. Follow the path and you'll find the platform with the jar. Interact with the jar to get the effect.

Eyeball
Enter the bluish-grey door in the Nexus. Go south-west and pass between two gravestones. There is an eyeball floating around to the south-west--interact with it to get the effect.

Hat
Enter the white door in the Nexus. Go north-west until you reach a swirl. Go immediately north and interact with the dress stand with the hat to get the effect.

Old Man
Enter the bluish-grey door in the Nexus. Go south-east until you find a geometric floating NPC. Interact with it to be teleported to Wasabi Hell. Navigate the maze until the pace opens up into an area with a hand figure at the top. (You know you're headed in the right direction when you have to lure a chaser out that's blocking the way.) Interact with the hand, then head north-east and interact with the tricolor lump (the one at the right). Doing so will teleport you to an area with bottles. Head north-west and interact with the bottle that has おさけ on it to get the effect.

Plain White
Enter the white door in the Nexus. Go north-east and pass through two angel wings. You'll be teleported to a calendar. Go to the white space at the end of the month. Then proceed south-east and interact with the trident. To the left of where you wind up is a crying lump - interact with it to get the effect.

OR

Enter the yellow door in the Nexus. Go south and interact with monochrome swimming NPC. In a monochrome location go north-west and pass through two big monochrome creatures. Then enter the door and go to right passage. In the room enter the mouth doorway. Go south and interact with crying lump.

Paper Bag
Enter the door in the Nexus that doesn't look like a door, then choose the pink door. Then proceed north-east and interact with the red heart. Go south and enter the rainbow-colored door. In the next area, go south-east through the gap in the purplish borders. Then head north-east until you reach a red crying head. Enter the mouth and go right until you reach a vomiting NPC. Interact with it to get the effect.

School Uniform
Enter the door in the Nexus that doesn't look like a door, then choose the dark red door. Go north and north-east on the path until you reach a heart-shaped area. Proceed to the upper right and interact with the pink orb. Then head up and interact with the blue orb. You will be teleported to the entrance to a room. Inside, toggle the light switch next to the door but also enter and go out from this room (just like in Yume Nikki). You will likely have to try this several times before you successfully trigger an uboa-like event. Then interact with the transformed NPC to be teleported to an isolated platform in the area where you got the Jar Effect. Interact with the NPC here and proceed west to a room with another Kizutsuki. Interact with her to get the effect.

Floating Head
(The Wings Effect is required.) Enter the door in the Nexus that doesn't look like a door, then choose the light blue door. Go north-east and enter the house at the top of the dirt patch. In the next area, keep heading south until you reach a platform with a cube in the center. Go in either side of the cube. Once inside, equip the Wings Effect and interact with the NPC to get the effect.