Tertullian

The Apology

Chap 22:

The philosophers acknowledge there are demons; Socrates himself waiting on a demon's will. Why not? since it is said an evil spirit attached itself specially to him even from his childhood-turning his mind no doubt from what was good. The poets are all acquainted with demons too; even the ignorant common people make frequent use of them in cursing. In fact, they call upon Satan, the demon-chief, in their execrations, as though from some instinctive soul-knowledge of him. Plato also admits the existence of angels. The Magi, no less, come forward as witnesses to the existence of both kinds of spirits. We are instructed, moreover, by our sacred books how from certain angels, who fell of their own flee-will, there sprang a more wicked demon-brood, condemned of God along with the authors of their race, and that chief we have referred to.

Chap 22:

Moreover, if the Magi call forth ghosts, and even make what seem the souls of the dead to appear; if they put boys to death, in order to get a response from the oracle; if, with their juggling illusions, they make a pretense of doing various miracles; if they put dreams into people's minds by the power of the angels and demons whose aid they have invited, by whose influence, too, goats and tables are made to divine,-how much more likely is this power of evil to be zealous in doing with all its might, of its own inclination, and for its own objects, what it does to serve the ends of others!

The Prescription Against Heretics

Chap. XL:

No Difference in the Spirit of Idolatry and of Heresy. In the Rites of Idolatry, Satan Imitated and Distorted the Divine Institutions of the Older Scriptures. The Christian Scriptures Corrupted by Him in the Perversions of the Various Heretics. The question will arise, By whom is to be interpreted the sense of the passages which make for heresies? By the devil, of course, to whom pertain those wiles which pervert the truth, and who, by the mystic rites of his idols, vies even with the essential portions of the sacraments of God. He, too, baptizes some, that is, his own believers and faithful followers; he promises the putting away of sins by a layer (of his own); and if my memory still serves me, Mithra there, (in the kingdom of Satan) sets his marks on the foreheads of his soldiers; celebrates also the oblation of bread, and introduces an image of a resurrection, and before a sword wreathes a crown.

On Baptism. II

Chap. V:

For washing is the channel through which they are initiated into some sacred rites--of some notorious Isis or Mithras. The gods themselves likewise they honour by washings. Moreover, by carrying water around, and sprinkling it, they everywhere expiate[7] country-seats, houses, temples, and whole cities: at all events, at the Apollinarian and Eleusinian games they are baptized; and they presume that the effect of their doing that is their regeneration and the remission of the penalties due to their perjuries.

Against Marcion

I. Chap. 13:

The Lions of Mithra are represented as types of an eager and impetuous nature.

The Chaplet, or De Corona

IV. Chap. XV:

Blush, ye fellow-soldiers of his, henceforth not to be condemned even by him, but by some soldier of Mithras, who, at his initiation in the gloomy cavern, in the camp, it may well be said, of darkness, when at the sword's point a crown is presented to him, as though in mimicry of martyrdom, and thereupon put upon his head, is admonished to resist and east it off, and, if you like, transfer it to his shoulder, saying that Mithras is his crown. And thenceforth he is never crowned; and he has that for a mark to show who he is, if anywhere he be subjected to trial in respect of his religion; and he is at once believed to be a soldier of Mithras if he throws the crown away--if he say that in his god he has his crown. Let us take note of the devices of the devil, who is wont to ape some of God's things with no other design than, by the faithfulness of his servants, to put us to shame, and to condemn us.

Tertullian.Apology. VIII: Those who aspire to initiation first I believe approach the father of the ceremonies to learn from him the preparations that are to be made.