The Wither King

The Wither King is the of The Master Catacombs - Floor VII.

Boss Fight
The bottom of Master Mode Floor VII contains a giant throne room. There are five relics placed next to dragon statues around the room. There are also five cauldrons in front of the throne near the centre of the room. They each have a specifically coloured clay below them. The players must bring and place the relics with the same corresponding colour as the cauldron's block of clay. By doing so, The Wither King will be summoned on his throne.

Damage cannot be dealt towards The Wither King, and he mostly acts as a spectator to the battle. The Wither King spawns five dragons named Apex Dragon, Flame Dragon, Ice Dragon, Power Dragon and Soul Dragon, with each dragon having a special ability. All five dragons must be killed near their corresponding coloured dragon statue to destroy them. All dragons can respawn at any time indefinitely until all dragon statues are destroyed. If all five statues are destroyed, the floor is completed.

If all five dragons are alive within at least ten seconds at any time, the Wither King will send the players into the air in the centre of a ritual. The dragons will complete the ritual and summon a giant hand coming up through the floor, grabbing and closing around the players, causing them to fail the dungeon run.

Appearance
The Wither King appears to be a Giant Wither in its invulnerable state with six tentacles coming out of its body.

Trivia

 * The Wither King's real name is Kaeman, confirmed by himself during his conversation with Necron in the Journal Entry - The Apprentice 3.
 * The tentacles coming out of The Wither King's body could be based off of the Wither Storm from Minecraft: Story Mode.