Dark Star X

Dark Star X is the sixth boss class located in the Gauntlet, which is inside the Challenge Node. It is the second-strongest boss in the game (after Bowser X). To start, 2500 coins must be paid to battle Dark Star X. It fights along with Dark Satellmite X's. The bros. have up to 12 turns to destroy Dark Star X. If the player defeats it, he or she will unlock Class 7, where they will fight all previous classes, including the Dark Star X, and Bowser X.

During the battle, Dark Star X is similar to the original Dark Star, only stronger and with a different color scheme. In the DS version, it has a red and black color scheme. In the 3DS remake, it has a yellow and purple color scheme.

Some changes are that the Dark Satellmites X's energy beams travel and Kamikaze attacks move faster, just as the Dark Star's clones do; there are also always seven clones (or nine, with sufficient damage) and they disappear earlier. When the bros' shadows come to life, they always split in two, something the original Star only did when it had been weakened.

If fought under the recommended level 40, the ramming attack after the laser and the ultimate vacuum will often defeat the bros instantly, even if they’re at full HP.

Changes
In Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, Dark Star X and the Dark Satellmites X have been recolored yellow with purple eyes, rather than being red with blue eyes in the original version. The Dark Star now have its own battle theme.

Battle
In battle, the Dark Star X can not usually be damaged. To expose its vulnerability, the Mario Bros. must destroy the Dark Satellmite Xs that surround it. With sufficient damage, the Dark Satellmites X will use a Kamikaze attack that consists of throwing a bomb at one Mario brother, and throwing their own body at the other. Ordinarily, both will miss, but either brother can attack the projectile launched at him. If the bomb is attacked, it will explode, doing damage to either Mario or Luigi. If the Satellmite X is attacked, it will be knocked flying into the Dark Star X. After being hit in such a way twice, the Star will become vulnerable and immobile for a turn.

Attacks
One of the Dark Star X's attacks consists of it splitting into seven (or nine, with sufficient damage) as a thick fog fills the battlefield. Each Dark Star X then flies slowly at Mario or Luigi, vanishing into the fog as it draws near. Mario and Luigi must then counter this attack by using their hammers on the hidden fake Dark Stars exactly 2 seconds after they disappear.

In another attack, the Dark Star X will shine a bright light at Mario and Luigi, causing their shadows to come to life. The shadows will then move in a circle around the Dark Star X, which will attack them with beams of electricity. The Mario Bros. must jump to avoid the electricity that the Dark Star X shoots, as any damage done to the shadows will hurt the real Mario Bros. as well.

The Dark Star X may also send red and green energy balls into the air. It will then fly through these balls in order, sending them at the correspondingly colored Mario Bro. They may be avoided by jumping.

When the Dark Star X is immobilized, it will shoot out a simple laser at Mario or Luigi, depending on who attacked it last.

After receiving sufficient damage, the Dark Star X will use a laser attack that fills up the entire touch screen. Starlow will appear just before this attack activates, suggesting that Mario and Luigi grab on to her. When they do so, Starlow will fly up in the air (top screen) therefore avoiding the attack. After the attack is through, the Dark Star X will look up and attempt to ram into Starlow. The Bros. must release their hold on Starlow to avoid making contact with the Dark Star. This attack deals massive damage and may also inflict the Poison status.

Just before it is defeated, the Dark Star X will use a vacuum attack on both Mario and Luigi. This must be countered by pressing and  repeatedly or the brothers will take massive damage. After it uses this attack, the Dark Star X is defeated.

Names in other languages
Stella Oscura