Mr. X

Mr. X (ミスターエックス) is a fake identity of Dr. Wily's, which he used to mask his true identity in Mega Man 6. Mr. X is a mysterious billionaire of unknown origin that is the leader of the X Foundation. He sponsors the World Robot Alliance and is the sponsor of the 1st Annual Robot Tournament. In the beginning of Mega Man 6, he takes control of eight of the strongest Robot Masters in the final event of the tournament to help him conquer the world. Before he was revealed to be Dr. Wily in disguise, Mr. X mentioned that he was the one who manipulated Dr. Wily into helping him take over the world.

X Crusher
In Mr. X's Castle, Mr. X fights with an iron ball type machine called X Crusher (Ｘクラッシャー) that swings in the screen and shoots a purple ball that splits in two when it touches the floor, each part sliding a different direction. Mr. X seems to have motion sickness while using it. When the machine is destroyed, he flies out from it and reveals that he is really Dr. Wily before escaping to his Wily Castle.

Strategy
Stay to one side and attack it by using any weapon (Flame Blast is its weakness). Dodge the energy balls by jumping. A good strategy is to use a charge shot. The Rush Power Adaptor also sends the crush flying back if a charged shot is used, and deals 4 damage per hit.

Trivia

 * Just before unmasking himself, Mr. X cries out: "My plan for world domination has faild". This typo was fixed in the Mega Man Anniversary Collection.
 * Mister X is commonly used as a pseudonym for someone whose name is secret or unknown.
 * In the Mega Man comic by Archie Comics, a wanted poster for Mr. X appears in Rosslyn and Gilbert's police office. He is also mentioned in issue 48, where he was revealed to be responsible for recovering Dr. Wily from the destroyed third castle (it is also implied that Mr. X and Dr. Wily, at least in this continuity, are indeed different people).