"Danyangzi" Ma Yu is the eldest of the Seven Quanzhen Elders. He taught Guo Jing inner energy skills. He later died of illness.
Ma Yu is not skilled in martial arts because he focused on studying inner energy. He even claimed that his martial arts are even worse than The Seven Freaks of Jiangnan. However, he does know some Martial Arts, matching a blow from Huang Yaoshi, one of the most powerful martial artists (though it should be noted that The Big Dipper Formation was helping him). It is also likely he is fairly skilled in sword-fighting because he always carries a sword.
Ma Yu knows the Big Dipper Formation and his power is enhanced with it.
Ma Yu is skilled in terms of inner energy.