|“|| I'm just following your example Castiel, how many did you kill in Heaven, during the fall..? Oh... you didn't know, a host of angels died when they fell. Azrael, Sophia, Ezekiel died. It doesn't even describe it.
Malachi was one of the many angels that fell due to Metatron's spell. After the fall, he formed a faction of angels and killed the angels who refused to join. Like many angels after after the fall, Malachi was angry towards Castiel due to his grace being stolen and him unknowingly having a part in Metatron's spell and was also looking for him. During this time, His rivalry , with Bartholomew began and his forces began, his forces attacked Bartholomew's men while they were at a bar. Like Bartholomew, Malachi also wanted to overthrow Metatron and reclaim Heaven Malachi later met with Bartholomew's representives agreeing that they would have to unite to take down Metatron. However, Malachi felt disrespected that Bartholomew wasnt at the meeting. Bartholomew's representatives later responded by calling him and his forces "street thugs" causing Malachi and his forces to kill the representatives declaring war over who would reclaim Heaven and take down Metatron.
During this time, Malachi manage to capture Castiel while following an angel who visited him in a motel. Malachi had the angel killed and tortured and interrogated Castiel about Metatron's spell. During this time, Malachi of tuanted him. Afterwards, Castiel escaped and killed one of the angels, stealing his powers. Is it later revealed that Malachi was murdered by Gadreel.