The Safety Deposit Box Dimension opens only once every 100 years. It's opening today. Yo needs the Toilet Brush of Illumination to fight the Night Master. The Night Master shrinks Yuck and puts him into Yo's body, so he can wait until Yo grabs the brush before emerging to claim it. Yin and Yang see Yuck enter Yo's body and have to stop him by shrinking themselves and entering into Yo's body to stop Yuck.