The Wither Dragon (also called Witherdragon or Corrupted Wither) is the boss of BlackDown. They are the equilivant of the Ender Dragon of The End. In order to fight it, the player must first defeat the Ender Dragon and Ender Steve.
The Wither Dragon was origonally a normal three-headed Wither boss. But this Wither was smarter than the rest of the history of Withers and they found a BlackDown portal. They didn't know what was inside, so they jumped in. When they first touched the alienoid ground, they began to morph. The three heads became one, they grew much larger, they grew wings, a tail, limbs, and colouring until they were...well...a Corrupted Wither/Wither Dragon. It was three times as smart than a normal Ender Dragon, and it vowed to destroy all humans.
The Wither Dragon's style of attack is very different than an Ender Dragon's. They can breathe fire and lava, which are yellow-green and are unaffected by Fire Resistance potions or armour. They stay high in the air and unsheath their claws and bat at the player like a cat. They have the same health as a normal Wither. They can swing their tail around and if the spike manages to hit the player, it will receive the Deadly Wither effect. It is similar to Cave Spider poison and Wither poison, but it goes much faster (x3) and can kill the player. The only way to prevent this is when you receive the Deadly Wither, drink a bucket of water and it will be reduced to Cave Spider poison.
When defeated, the Wither Dragon death animation will play and a shower of XP orbs will fall from the sky, as well as a WitherBlade, the 3rd strongest sword in the game.