Spoiler alert: The following section contains plot-specific details.(Skip Section)
The one who summoned the invader from another dimension was none other than Taranza, who plotted while hidden in apparent defeat. He has summoned the giant mirror as his final weapon, gazing not only upon its shimmering surface but the dark shadows lurking within...”
The black mirror resembles a darker, more sinister version of the original Dimension Mirror. Instead of wing and feather designs, it is adorned with numerous spikes and stars, with two of the spikes curving upward to resemble horns. The mirror itself appears onyx with some hints of silver, contrasting the Dimension Mirror's golden color scheme.
The origins of the black mirror are unknown. Taranza presumably found it before the game's events, as he is under its influence for the entire story. In his corrupted form, he summons legions of powerful enemies to besiege the Dream Kingdom.
As a last resort when cornered in the Decisive Battlefield, Taranza summons the black mirror to use against Team Kirby. Dark Taranza emerges from it and does battle with the team; when defeated, he calls up the black mirror and summons the king of darkness, King D-Mind. He destroys Dark Taranza and assaults Team Kirby. The heroes challenge him, return him to the mirror, and destroy it--this traps the king in a sealed-off dimension in the process.
With the mirror shattered, Taranza comes to his senses and becomes a passive member of the village. Peace returns to the Dream Kingdom and Team Kirby vows to suppress any threats that should emerge.
And so, the king of darkness—who sprang from the ugliness of the black mirror—has been sealed in a far-off dimension by Team Kirby. Taranza is now free of the mirror's magic and has returned to normal. Now, at last, peace will return to the Dream Kingdom...”
The black mirror is gone, and peace is finally, truly restored to the land! You faced so many hardships. I know it wasn't easy... After all of the battles you fought for the people of this kingdom, you have my gratitude, and my respect. Your deeds will surely go down in history. No, they'll become legends! For all you've done, I truly thank you!”
It is unknown if this mirror leads to the same world that the Dimension Mirror leads to.
Parallel Susie's mech sports the same eye insignia as the one found on King D-Mind's hammer and clothing. This suggests a connection between the two, which could indicate that Parallel Susie has some tie to the black mirror.