Luigi on the Roof
From the Super Mario Wiki
Luigi on the Roof is the sixth and final mission of Good Egg Galaxy in Super Mario Galaxy. This mission is only accessible after receiving a letter from Mailtoad after finishing Luigi and the Haunted Mansion telling Mario (or Luigi) about Luigi being trapped on the roof. The primary goal in this mission is for Mario to access the top of the roof of the starting planet to rescue Luigi. This mission can be completed on any of the galaxy's non-comet levels.
Mario first lands on the grassy starting planet. Here he has to navigate around some blue Electrogoombas. Eventually, he finds himself on the bottom of the starting planet. Whilst here, he finds an orange Warp Pipe that takes him inside a secret room inside the planet. This room is filled with Boulders. Mario first has to find a ramp that takes him to the rightmost wall of the area. He then navigates to the back wall of the area by walking across another ramp. A third ramp takes him to the leftmost wall of the area, whilst a fourth one takes him to the top of the room. Here there is an orange Warp Pipe. This Warp Pipe takes Mario to the roof of the house where Luigi is trapped. Talking to Luigi reveals the Power Star of the mission.
Names in other languages