This stage, hence its name, is a UFO. There is a play switch in it that turns it upside down. The goal is upside down when the UFO is upright. Some bananas are placed on top of the UFO while some of them are placed inside it.
To get to the goal, roll into the UFO, and activate the play switch. Keep your balance by pushing down-left on the control stick as soon as you are on the UFO's left side, and roll into the goal immediately; because if you move too slowly, the UFO will turn upright, making it where you will need to activate the switch again. Be careful not to fall through the hole when the UFO is upside down.