Poniko is a well-known character appearing in Madotsuki's dream.
She, like Madotsuki herself, lives alone in a very bare house. She seems to want to be alone, as Madotsuki is only able to reach her house by going through a Pastel Lake.
No matter what you do, she doesn't seem to pay any attention to you, which is the point of some fandom hilarity. The only exception to this is the light switch.
If you turn off the light, there is a 1 in 64 chance that you will see Uboa.
Uboa is usually referred to as male, and is probably the main reason most people started playing Yume Nikki. He jumps out as soon as you turn off the light, and makes a strange 'whaaaa' sound, surprising many people.
If you touch him, he'll send you to a dead-end room with white water, red sky and a strange monster in the background.