Origin : From Mastim (Hebrew) the Hiphil participle of Satam which means 'one who is adverse' or 'inimical.'
Myths : Mastema helped with one tenth of the spirits who rebelled against God, has the mission of tempting men to sin and accusing them before the Throne of God. He is said to have helped the Egyptian sorcerers achieve their wonders and urged the Egyptians to pursue after the children of Israel.
Source: The Book of Jubilees, Fragments of a Zadokite Work.
Association : Satan
"When Mastema, the leader of the spirits, came, he said: 'Lord creator, leave some of them before me; let them listen to me and do everything that I tell them, because if none of them is left for me I shall not be able to exercise the authority of my will aong mankind. For they are meant for (the purposes of) destroying and misleading before my punishment because the evil of mankind is great.' Then he said that a tenth of them should be left before him, while he would make nine parts descend to the place of judgment." - Jubilees 10:8-9
"And they made for themselves molten images, and they worshipped each the idol, the molten image which they had made for themselves, and they began to make graven images and unclean simulacra, and malignant spirits assisted and seduced (them) into committing transgression and uncleanness. And the prince Mastema exerted himself to do all this, and he sent forth other spirits, those which were put under his hand, to do all manner of wrong and sin, and all manner of transgression, to corrupt and destroy and to shed blood upon the earth. For this reason he called the name of Seroh, Serug, for every one turned to do all manner of sin and transgression. - Jubilees 11:4-6
"And the prince Mastema stood up against thee, and sought to cast thee into the hands of Pharaoh, and he helped the Egyptian sorcerers, and they stood up and wrought before thee the evils indeed we permitted them to work, but the remedies we did not allow to be wrought by their hands." - Jubilees 48:9-10
"And notwithstanding all (these) signs and wonders the prince Mastema was not put to shame because he took courage and cried to the Egyptians to pursue after thee with all the powers of the Egyptians, with their chariots, and with their horses, and with all the hosts of the peoples of Egypt." - Jubilees 48:12
"For on this night -the beginning of the festival and the beginning of the joy- ye were eating the passover in Egypt, when all the powers of Mastema had been let loose to slay all the first-born in the land of Egypt, from the first-born of Pharaoh to the first-born of the captive maid-servant in the mill, and to the cattle." - Jubilees 49:2