High above the sky lies the Midair Stadium, a prestigious venue where the biggest events in the Nintendo multiverse are held. Today, a huge crowd has gathered to watch a match between Mario and Kirby, two experienced fighters with massive followings. Two princesses make a special guest appearance: Princess Peach and Princess Zelda. The match is so popular that even a certain angel high in Skyworld is spectating the match. However, what started out as a friendly battle between two seasoned veterans will soon be the start of a new global threat...
The big fight
You'll first play a battle in which Mario takes on Kirby. You get to choose which character you want to fight as, and both players will get the same characters and be on the same team in two-player mode. The objective is simple, take a stock off your opponent. This is just a standard match against a single opponent, and your higher amount of stocks gives you a big advantage. You should be able to win the match without much effort, and only lose a stock or two on higher levels.
Shadow Bug invasion
After the battle, Meta Knight's ship, the Halberd, will appear and drop of a payload of Shadow Bugs, which form into an army of Primids. Peach and Zelda will join Mario and Kirby to fend off this threat, giving you four characters to choose from. The battle that follows is a free-for-all against tons of enemies. Other than the normal Primid, which only use melee attacks, there's also Boom Primids, who can throw projectiles, Sword Primids, who have longer reach, and Spaaks, clouds that shoot electricity at you. The Spaaks are the biggest threat as their attacks do high knockback and they get more powerful at low life, but you can dispatch them more quickly by attacking the battery on their backs.
Once you finish of the squad of Primids, the Acient Minister flies in and deposits a subspace bomb with a time of three minutes. Mario tries to investigate, but he is blasted out of the stadium by a cannonball shot from Petey Piranha's mouth. Petey then captures the two princesses, so Kirby alone will have to defeat him.
Petey is an easy boss, he only has two attacks. For his first attack, he scrapes one of the two cages on the ground. Avoid this by jumping. He jumps up in the air and drops with devastating force for his second attack. On harder levels, avoid this at all costs! It can be an 1-hit K.O. Aside from that, he's really easy.
After you beat Petey, Wario appears, holding a Dark Cannon, which he shoots at the princess that you don't rescue and is in a more helpless position (much to Wario's pleasure). Kirby and Peach/Zelda try to pursue Wario, but the subspace bomb has but five seconds left, so Kirby calls for his Warpstar, and with Peach/Zelda in tow, they make it out in the nick of time. Meanwhile the stadium is sucked into subspace.