Miracle Knee! is a technique used by Mr. Satan to back out of having to fight opponents stronger than him by crouching down clutching his stomach pretending to suffer from stomach pains (usually proclaiming something like, "Aw, My Stomach! It Hurts!" or something along those lines) while maintaining his reputation as the Champion of Martial Arts. It was first used during the Cell Games as Mr. Satan's excuse to Jimmy Firecracker and his students not to fight powerful Cell and was named in Dragon Ball: Xenoverse.
It is one of Mr. Satan's often used excuses for not having to fight those stronger than him which was born a personal vow Mr. Satan had made to himself not to fight any one who seemed crazy strong, after he was injured in an encounter with Mercenary Tao which resulted in the death of the Master of Satan Castle, Mr. Satan's martial arts mentor. It is also a way for Mr. Satan to back out of a fight while at the same time saving face with the public (save for those who know better such as the Z-Fighters) and maintain his reputation with the public's false belief that he is unable to fight at full strength due to suffering stomach pains. As Mr. Satan has used it several time he has lead the public to believe he suffers from a chronic stomach condition. It is just another example of Mr. Satan's ability to deceive his public.
It was originally used by Mr. Satan as an excuse for why he couldn't join the fight, though in the anime his assistant Miss Piiza foils it slightly when she reveals she keeps stomach ache medication in her cleavage.
Video Games Appearances
"Crouch down as if kneeling to avoid an attack."
— Dragon Ball: Xenoverse in-game description
In Dragon Ball: Xenoverse, it is Mr. Satan's evasive skill where the user crouches down to avoid an attack. It is also Videl's evasive skill in her 6th skillset and as Krillin's Evasive Skill in his 1st skillset. It can be obtained by the Future Warrior in Parallel Quest 17: "Challenger Hercule". It also appears as one of the Future Warrior's Emote Actions under Emotes Option 30: Stomach Ache.
Mr. Satan's equipable "Master" Z-Soul, "Eek! Waaaah! What'll I do?!" is activated by the skill when it is used in battle, which nulls all attack power (the users Basic ATK, Strike Supers, and Ki Blast Super stats) while granting temporary invincibility.