The treasure chest was the prison of Dark Nebula, ruler of the underworld. Kirby (Franchise)/Meta Knight knew the secret of the chest. He fought Kirby to prevent Dark Nebula from being released.
Dark Nebula is the final boss of Kirby: Squeak Squad. Having been sealed away in a Treasure Chest, it was accidentally unleashed upon the world by Kirby (Franchise)/Daroach, who it took possession of.
At some point prior to the events of Kirby: Squeak Squad, Dark Nebula was sealed in a chest due to its evil power, and seemingly forgotten.
Through unknown circumstances, the chest was in possession of King Dedede at the beginning of the game itself, who was seemingly unaware of its contents.
However, Daroach somehow became aware of the chest's power and accosted it from King Dedede's castle, believing it to be the source of ultimate power[citation needed]. After being stolen by Meta Knight, who actually appeared to have an idea what was in the chest, and subsequently Kirby, who thought it contained his strawberry shortcake that had been stolen earlier, the chest was seized by Daroach, who promptly opened it. Daroach is quickly possessed by Dark Nebula and turned into Dark Daroach, and then flees with the Squeaks into the depths of Gamble Galaxy.
Kirby chased Dark Daroach and defeated him, expelling Dark Nebula in the form of a black star with two smaller stars in close orbit: Kirby, now toting the Triple Star that Daroach dropped, chases Dark Nebula still deeper into Gamble Galaxy until both arrive at a crystalline battlefield. Here, Dark Nebula begins gathering small and dark core stars, which assimilate into its being until he gains his true form, Dark Nebula is then fought. Once defeated, it begins disintegrating core star by core star, until the only thing left is an eye, which promptly explodes.
Star Attacks: Dark Nebula's main form of attacking is launching stars at the opponent from an angle (usually the side of the arena).
Form Change: Dark Nebula also has three alternative forms. While changing forms, the screen will flash white.
Status Effects: If the opponent bumps into Dark Nebula, they'll be damaged (burned, frozen or electrocuted depending on what form Dark Nebula has).
Fire: In its fire form, it can shoot stars that can burn the opponent. Its strongest attack in this form is releasing a large fireball that slowly approaches the ground and explodes, thus creating a vertical fire-blast. On the sides of the blast are rows of lingering flames. Also in this form, it will move at great speeds in angles.
Thunder: In its thunder form, it will shoot stars at the opponent that can shock them. Its physical attack involves moving in a zigzag pattern. Its strongest attack is releasing four electric streams diagonally in all directions, then discharging them to create an electric frame that covers all sides of the arena.
Ice: In its ice form, it shoots out stars that can freeze the opponent. Its physical attack involves going around the arena in a circle. Occasionally while doing this, it will float back and forth across the stage in an arc. Its special attack is firing an ice laser at the ground, thus freezing it. This hinders the opponent's traction so that Dark Nebula's attacks can't be dodged as easily.
Other
Standard Tactics: Dark Nebula instantly goes for possessing someone, if his possession fails he will form together and use elemental attacks along with star projectiles.
Weaknesses: Nothing notable.
Trivia
The symbol for the Triple Star shows three stars, one blue, one green, one red, and these are also the colors of Dark Nebula's forms. This shows that, like the Triple Star, he uses the power of the three elements–fire, thunder, and ice–which are emphasized more in Kirby: Squeak Squad than in any other game.
In the ending of Kirby: Squeak Squad, Dark Nebula has the title of "ruler of the underworld." In the Japanese original, his title is 「あんこくのしはいしゃ」 (ankoku no shiwaisha), which translates to "ruler of darkness." This is possibly a mistranslation, as the word for darkness, あんこく (ankoku), is also used in the word for the underworld, あんこくがい (ankokugai).
Dark Nebula's behavior has a passing resemblance to that of Miracle Matter. Dark Nebula is also noted to be similar to the Dark Matter group in the Japan-exclusive 20th Anniversary Kirby of the Stars Dream Land Encyclopedia, although it also states that is is unclear if they're connected.
It is not known what Dark Nebula had intended to do once he had possessed Daroach and the Squeaks. However, due to the final battle between Kirby and Dark Nebula taking place deep within a previously unseen black hole near Planet Popstar, it is possible that Dark Nebula may have been trying to destroy the planet.
Official artwork depicts Dark Nebula's eye as a purple color. However, its in-game sprite has its eye colored more of a burgundy and maroon color.
Its official art is corrected in 20th Anniversary Kirby of the Stars Dream Land Encyclopedia to resemble the in-game colors.
Dark Nebula reappears as a cameo in Kirby Star Allies as a Stone transformation, this time peeking out of a Treasure Chest, and as part of the Smack-in-the-Box attack by Daroach after summoning and opening a big blue Treasure Chest that springs out a fake Dark Nebula. It also appears as a symbol on Void Termina's body and as a drawing Daroach draws in the ending for the 2nd wave Dream Friends.
Dark Nebula resembles Starro from DC Comics, being a purple star with a single eye at its center. Incidentally, Starro also has mind control powers.
