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.

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.