Dark Meta Knight

Dark Meta Knight is an evil mirror version of Meta Knight. While Meta Knight is chivalrous and honorable, Dark Meta Knight is vicious and brutal. He appears as the secondary antagonist in Kirby and the Amazing Mirror and the main antagonist in Kirby: Triple Deluxe 's Dededetour story mode, as well as the Bigger Bad of the game overall.

Kirby & the Amazing Mirror
He is first encountered when he slashes Kirby into four different colored Kirbies. Dark Meta is then seen defeating Meta Knight and sealing him within the Dimension Mirror, shattering it to prevent Kirby from being able to reach him. The second time he appears he he is disguised as Meta Knight and fights Kirby. Once he is defeated he retreats. The third and final time he is fought is within the Dimension Mirror. He again attempted to disguise himself as Meta Knight to fool Kirby, but the real Meta Knight reveals the impostor. Dark Meta Knight then assumes his true colors and fights Kirby. When he is finally defeated his body shatters and a portal opens up leading to the true mastermind, Dark Mind.

Kirby: Triple Deluxe
Although Dark Meta Knight does not appear in person until Dedede Tour has been unlocked, it is strongly implied that he is the main antagonist of the entire game (instead of Queen Sectonia), or at least the Bigger Bad, as he was in control of the Dimension Mirror the entire time, which was responsible for corrupting Sectonia and turning her evil.

Sectonia was once a just and kind ruler of Floralia and a close friend of her right-hand man Taranza, who eventually came across a mirror which he then presented to her. She soon became obsessed with both the Mirror itself and her own beauty and vanity. Little did she know that Dark Meta Knight was the new master of the Dimension Mirror and was casting a negative influence on her. She eventually used her newfound dark magic (presumably obtained through Dark Meta Knight's manipulation) to transform herself into a giant bee, seeing her new form as true beauty. The more evil Dark Meta Knight fed her through the mirror, the worse she became towards Taranza and her citizens. She eventually tried to rule over Floralia's inhabitants as their goddess and began imprisoning them to serve her.

Dark Meta Knight finally appears in person as the hidden true main antagonist and final boss of Dedede Tour. After the defeat of Dark Meta Knight's pawns, Sectonia (in her DX form), and Shadow Dedede, King Dedede traveled into the Dimension Mirror and encounters Dark Meta Knight, who is now far more powerful than before, no longer working for Dark Mind, and is in full control of the Dimension Mirror. Dark Meta Knight is a considerably greater threat in his reappearance, being able create clones of himself and dispense mach tornado's freely. Once he is defeated, he is sealed within the Dimension Mirror, which King Dedede then smashes.

He also appears as the penultimate foe in The True Arena. Upon Kirby destroying him a second time, he violently shatters like glass,  leaving Kirby to destroy Sectonia Soul (who is still under Dark Meta Knight's evil power and influence, although his physical body is destroyed) however, as Dark Meta Knight had been destroyed before in the same way by Kirby, it is likely that he will make a return.

Trivia

 * Dark Meta Knight is the Bigger Bad of the main story line of Triple Deluxe, since his Mirror was what corrupted Sectonia and made her vanity-obsessed.
 * Although Dededetour and The True Arena are considered non-canon, this does not change the fact that he is canonically the hidden mastermind of the main story line.