Mafia Land Alliance vs. Carcassa Famiglia is a battle on Mafia Land fought between the Mafia Land Alliance, consisting of the Vongola Famiglia's Vongola Decimo, his right-hand man, his Rain Guardian, and his home tutor, the Difo Famiglia, the Nuovo Famiglia, the Beccio Famiglia, and many other unnamed Famiglias versus the Carcassa Famiglia's forces led by the Cloud Arcobaleno, Skull, and his subordinates.
Tsuna, his mom, Bianchi, I-Pin, Lambo, Reborn, Gokudera, and Yamamoto go to Mafia Land, a popular Mafia vacation spot allowing only Mafia Famiglias that do not deal in drugs, crime, and other corrupt activities. However, when there, Skull, paid by the Carcassa Famiglia to attack Mafia Land, attacks, as the Carcassa Famiglia mafioso wasn't allowed to set foot on the island due to their Famiglia's corrupt activities.
Skull's forces arrive at the island and prepare to attack. Meanwhile among the Mafia Land Alliance, the Difo, Nuevo, and Beccio Famiglia argue over who was going to take command. Suddenly, Gokudera pushes through the crowd (calling Tsuna "Decimo"), causing members of the three arguing Famiglia to furiously ask Gokudera why he made "Decimo" sound so important. Gokudera proudly retorts that "Decimo" was the 10th boss of the Vongola Famiglia, causing the other three Famiglias as well as the other Famiglias unanimously agree that the Vongola should lead them, and no one could compare to them. As a result, other Famiglia members carry Tsuna out to the front lines, other Famiglia members attacking Skull's subordinates head-on. Tsuna and Reborn run into Skull. Skull expresses his surprise at Reborn and Colonnello's presence, and Reborn makes snide jibes towards Skull about his "lackey" status. Skull grows angry and captures Reborn with his Animal Partner, an octopus named Oodako who follows Skull's finger movements as commands. Reborn, however, shoots Skull's left hand with a Dying Will Bullet, enlarging the hand. Skull waves it off, stating that he could still control Oodako with his right hand, but Reborn reveals that since Oodako didn't recognize the command, it was berserk. Sure enough, Oodako began wildly flailing due to confusion and released Reborn. Reborn punches Skull into a tree. Skull weakly gets up, stating that he would blow up the entire island. Reborn replied, however, that it wouldn't be happening, as Colonnello was present. Colonnello then blows up all of Skull's battleships, finishing the battle. At the general battling area, the Mafia Land Alliance wins over Skull's side.
Afterwards, Tsuna finally received his entrance pass, but Nana informed him that it was time to return home, much to both Tsuna and Gokudera's dismay, as they were both incarcerated in the re-training area of Mafia Land.
- In the manga, the battle against the dojo busters occurred before this Mafia Land battle; however, in the anime, it occurred after.