Metal Face is the primary main antagonist of the original Xenoblade Chronicles game, he is the main reason Shulk joined the Bionis in their journey.
Leading the raid against Colony 9, Metal Face is the one who "kills" Fiora, causing Shulk to mark Metal Face as his rival. Shulk's primary motivation throughout the first half of the game is to kill Metal Face once and for all. During the battle it is revealed that Metal Face is immune to the Monado's effects, making him an incredibly dangerous adversary. During this sequence he mocks Shulk with a wag of his finger. Metal Face also gravely wounds Colonel Vangarre in the assault. He eventually flees the raid, withdrawing his troops.
Metal Face is mentioned later by Xord as having "scarpered". As Xord continues his efforts against the Monado's wielder, Shulk, Metal Face is repaired from his earlier battle and now has a voice and working mouth.
After Xord's explosion and the brief lift ride to the surface, Metal Face immediately attacks with an army of Xord Replicas and Mechon Models M64X and M53X. Just as things look grim for the party, Dunban and Dickson appear to fight off Metal Face's army. During the scarper Metal Face taunts the fighters, telling them the Monado does not work for a "bunch of losers" and how much he enjoyed Fiora's screams of pain. Just as he is about to strike the finishing blow, a strange bird appears and attacks him, allowing the Monado to cut into his limbs. Taking this as a sign to flee, Metal Face takes off, leaving a frustrated Shulk and Reyn.
During a premonition, Shulk envisions facing Metal Face atop a huge tower (later revealed to be Prison Island), and winning the fight. This is what drives them to continue up Bionis.
Metal Face appears with a new weapon which looks like a spear that can suck out Ether out of a life form (such as a Homs or a High Entia). When the group arrives at the top of Prison Island, Zanza allows Shulk to upgrade the Monado. As Zanza is allowing Shulk to upgrade the Monado, Metal Face throws the spear which pierces Zanza in the chest, killing him. He also kills Sorean while he was protecting Melia. Just before Zanza dies, he tells Shulk that the process is complete and Shulk transforms the Monado into the Monado II. Using it, he fights Metal Face. After the battle, Shulk manages to cut off Metal Face's left arm. As he is about to finish Metal Face off, Silver Face (Face Nemesis) protects Metal Face and it is shown that Fiora is still alive. Silver Face/Face Nemesis flies off and Metal Face follows with the Mass-Produced Faces.
At one point during the showdown, Metal Face hints at Dunban his identity through an attack with his claws, which Mumkhar also used. The shock on Dunban's face confirms he recognises this, but does not believe it could be his old friend. The moment is not mentioned afterwards.
When the group reaches near the end of Valak Mountain, Silver Face appears. As she is talking with the group, a laser shot hits the side of the Mechon and sends Silver Face crashing into a wall and knocking Fiora out. Metal Face is revealed to have fired the shot and the Mechon lands on top of Silver Face, telling Shulk to give him the Monado or he will kill her. At this point, Metal Face is revealed to be Mumkhar, an old colleague of Dunban's who ran off during the Battle of Sword Valley and was supposedly killed by Mechon. He emerges from his Mechon to claim the Monado, but is caught off guard by Melia and the group fights him. After the fight, Dunban and Mumkhar engage in an intense verbal and physical struggle, which culminates in Dunban managing to injure Mumkhar. Before they are able to finish him off, however, a golden Mechon appears to stop the fight and takes Fiora away, with Mumkhar in tow, while the group tries to chase after them.
As the group is trying to reach Galahad Fortress, Mumkhar appears and challenges them with eight Mass-Produced Faces (although strangely, only two Mass-Produced Faces and Mumkhar are present for the actual fight). After the fight, Dunban is just about to finish Mumkhar, but Shulk stops him, saying that he does not want to kill the Homs inside the Face Mechon. Hearing this, Dunban relents, but cuts off both of Metal Face's arms when Mumkhar attacks him from behind. He says that he disagrees with Shulk but is convinced with his words, telling Mumkhar that he does not have time to "play". Metal Face gets up and just tells them to die already. Shulk has a vision of a huge spear-like piece of rock falling and stabbing into Metal Face, thus killing Mumkhar. Shulk tells Mumkhar to stop but Mumkhar, consumed with frustration and hatred, is beyond listening, and fires his energy cannon at Dunban in one last effort to kill him. Shulk pushes Dunban out of the way and the shot hits a pillar on Galahad Fortress, shaking loose a spire from the structure, which falls and impales Metal Face, just as Shulk had foreseen. The force of the impact causes the platform they were fighting on to break off, with Mumkhar effectively nailed to it by the fallen spire, still alive and screaming as he falls into the abyss of the Great Sea. After Dunban takes a moment to lament Mumkhar's foolishness, the group then moves on into Galahad Fortress.
In Project X Zone 2, Mumkhar's soul reincarnates in the faced Mechon's body thanks to the Golden Chains' power, during the whole game, he plans to gain more power and go after Dunban once again and finally kill him; however, he is killed again by Fiora's group alongside Kamuz, Sigma, Pyron, Ranmaru, Ouma and Byakushin.
Crosspedia Entry (Project X Zone)
One of the Mechonis machinery life forms known as "Mechons", this unit is used exclusively by the powerful warrior Mumkhar. The entire unit is colored black.
Mumkhar once used it to attack Colony 9, seriously injuring Fiora in the process.
Metal Face's sharp and angular body is incredibly well-armored, and its attack power matches the ferocity of Mumkhar's own personality. Along with the slashes it makes with long, liquid-filled claws, it can also transform into flight mode and fire energy shots from its main cannon.
Other fanon appearances
He is one of the bosses of the game.
Metal Face appears as a Boss Unit.
He has a major role in the game, joining forces once more with T-elos (Xenosaga) and Deus (Xenogears). After KOS-MOS and T-elos became one being, he and Deus kept on fight until the game's final chapter.
Metal Face appears as the boss of Gaur Plains Stage.
Metal Face appears on this TV show, as well as the associated video game that was released for its 50th anniversary, virtually unchanged from his appearance in the canon Smash Bros. games: he is a stage boss on Gaur Plain. He now gifts the fighter who defeated him a treasure trove of power items, such as Golden Hammers, Heart Containers, and Master Balls, in addition to the massive explosion.