After witnessing the grim fate of the midair stadium, Pit is summoned by the goddess Palutena, who entrusts him with her sacred bow. She commands Pit to defeat the Subspace army, who has begun their invasion in Skyworld below.
Fall down to the bottom of the shaft, through the multiple clouds in the way, until you reach a stone structure. There are two blue item boxes nearby. These boxes contain items that you can obtain by attacking them. Get both item boxes, then move to the right. Jump up the ledge, get the third item box, then continue right until you reach your first door. Enter it to trigger a cutscene.
Attack on Skyworld
Standing on a floating rock, Pit spots the humongous figure of the Halberd ascending above the clouds. Tons of shadow bugs are dropped on to the ground, forming into an army of Primids. Surrounded by enemies, Pit splits his bow in two, using it as blades to fend off the attackers.
Starting off, Primids will be attacking you from all sides, but it won't take too much effort to defeat. Once you've taken care of the enemies, a staircase will appear to your right, letting you proceed forward. After a few Spaaks, you will find your first gold item box on a stone platform high above the ground. These item boxes contain special collectables and must be broken to obtain 100% completion.
Continue to the right and you will encounter a Cymul, floating metallic orbs that can reflect projectiles. Attack it up close to defeat it, then keep running to the right until you're attacked by a Greap. This scythe-wielding monstrosity can do a lot of damage with a single attack, but its scythes will get stuck in the ground after an attack. Avoid the scythes as they swing down, then roll behind the Greap and attack it while it's vulnerable. Its weakspot is in its head, so attack it to defeat it quicker. Once the Greap has fallen, you can enter the door to another part of the level.
Plumber and angel
Scouting out the field of clouds, Pit spots Mario's trophy in the distance. He hurries toward the trophy and quickly revives Mario. After recalling the events back at the stadium, Mario decides to join forces with Pit to clear out the remainder of the Subspace army at Skyworld.
Fall down the shaft until you spot several rolling wheels. These are Glunders, and they will attack you if you get too close. Just stay out of their way if you don't want any trouble, and drop down further until you land on a purple cloud. Stay on the cloud as it moves toward another section of the level, where you will be introduced to Jyks. Don't bother attacking these spike balls, as they're invincible, and just focus on evading them.
Keep moving to the right, taking out enemies along the way, until you reach a section of the level where columns rise out from the floor. The third column hides a door behind it, so wait until the column fully retracts, then enter it. Inside, break the blue item box and take its contents. The stage will start scrolling upwards, so keep climbing up the cloud platforms until the top stone platform. Once the stage stops scrolling, a blue item box will appear on the platform. Drop down and exit through the door to return to the main level.
Fight your way past the enemies as you continue to the right. You will soon be locked into a battle with multiple Primids and Spaaks. Once you take them out, a Roturret will appear. Destroy it quickly by repeatedly attacking it, as it won't have time to reorient itself for an attack if you hit it persistently. Once you defeat the Roturret, move right and ride the booster. You will land near the golden door, which marks the end of the level. Enter it to finish the stage.
Having reached the edge of Skyworld, Pit and Mario can only watch helplessly as the Halberd flies away in the distance. Suddenly, a lone Arwing shoots toward the Halberd, as if trying to bring it down.
After finishing the level, Mario and Pit will join your team.