Fog King

The Fog King is the primary antagonist of Xenoblade Chronicles: Future Connected.

Story arc
Shulk and Melia depart for Alcamoth using the Junks, when suddenly the ship is shot down by a laser and they crash on the Bionis' Shoulder. They decide to head to the Companions' Cape to learn more about what attacked them. At the cape, they are approached by a man named Maxis, who explains that they were attacked by a mysterious monster that recently appeared in Alcamoth, known as the Fog King, and that it's seemingly invulnerable to normal attacks. The Fog King forced Maxis and the rest of the High Entia to leave Alcamoth.

Shulk, Melia, Kino, and Nene arrive at Alcamoth, and they see a strange rift which they decide to investigate. The group runs into Teelan, who is being attacked by a Snowal Taos covered in fog, and they manage to defeat it. However, the Fog King suddenly emerges from the rift and the group attempts to fight it, however, all of their attacks are rendered useless against it, so they decide to retreat. Teelan explains that the Snowal Taos that attacked him is known as a Fogbeast, which are monsters covered in fog that like to follow the Fog King, he then tells the group to head towards Gran Dell.

Upon arriving at Gran Dell, the group runs into Radzam, who observes that there's a large amount of Telethia swarming Alcamoth, and they are feeding off the ether being produced by the Fog King, which is preventing the Fog King from leaving the city. The group then notices that a giant rift has appeared outside of Alcamoth. Shulk and Radzam eventually decide that they need to empower Shulk's weapon, the Monado Replica EX, so it can emit a dense ether field in order to make the Fog King vulnerable to attacks. After finding the materials, Shulk is able to upgrade his weapon to the Monado Replica EX+, allowing them to properly fight the Fog King.

The group returns to Alcamoth and battles against the Fog King. The rift grows larger, which makes the Fog King significantly stronger, but a bunch of Telethia fly into the rift and explode, which causes the Fog King's power to decrease and damages it. Melia is able to eradicate the Fog King, which also destroys the rift in the sky.

As a boss

 * Fog King (part 1)
 * Fog King (part 2)

Lore

 * The Fog King bears a striking resemblance to the Infernal Guldo from Xenoblade Chronicles 2, with many theorizing that the two may be connected in some way.