One of the most puzzling features of Marcion's antithesis is its seeming use of Matthew. We can see this in Dialogue Adamantius as in these two cases where verses in Matthew's Sermon on the Mount appear to show up in the Antithesis arguments of Megathius, the Marcionite champion:
// The third antithesis found in Dialogue Adamantius 1.12 / 8.12d
Megethius: The Lord brought to view in the Law say, ‘You shall love him who loves you and you shall hate your enemy.” (Leviticus 19:18 LXX with τὸν ἀγαπῶντά σε for τὸν πλησίον σου, Matthew 5:43) But our Lord, because He is good, says “Love your enemies, and pray for those who persecute you.” (Matthew 5:44; see also Luke 6:27-28)
ὁ δὲ κύριος ἡμῶν, ἀγαθὸς ὤν, λέγει·
ἀγαπᾶτε τοὺς ἐχθροὺς ὑμῶν καὶ εὔχεσθε ὑπὲρ τῶν διωχόντων ὑμᾶς.
Ἐν τῷ νόμῷ λέγει· ὀφθαλμὸν ἀντὶ ὀφθαλμοῦ καὶ ὀδόντα ἀντὶ ὀδόντος, ὁ δὲ κύριος, ἀγαθὸς ὤν, λέγει ἐν τῷ εὐαγγελίῳ· ἐάν τίς σε ῥαπίσῃ εἰς τὴν σιαγόνα, παράθες αὐτῷ καὶ τὴν ἀλλην.
But in truth we have it backwards. And here is why, and what it tells us: Marion's Antithesis was composed knowing the Marcionite Gospel and Apostolikon, which was paraphrased and compared with the Jewish Bible (Old Testament). The key here is paraphrased.
The first case from DA 1.12 is a paraphrase of Luke 6:27-28 compared with Leviticus 19:18 LXX, with the added phrase καὶ μισήσεις τὸν ἐχθρόν σου nowhere found in the bible. Perhaps this was inspired from the prior verse 19:17 οὐ μισέω ὁ ἀδελφός σύ ὁ διάνοια "you shall not hate the (your) brother in your thoughts," implying from that the opposite for your enemy. Somehow in Matthew the entire phrase appears in the exact order and form of the Antithesis and making the same argument as the Marcionites!
This is followed in Lukan order in DA 1.15 again paraphrasing Luke 6:29 compared to Exodus 21:24 (and parallels). Surprisingly this also appears in the same Antithesis form in Matthew 5:38-39.
That these same paraphrases show up in Matthew, tells us that Matthew must been written after the Antithesis, because it is a source, as we see above, with the conclusions adjusted to fit the competing Catholic theology. Much of Matthew's Sermon is of this nature, stating a Marcionite position, and correcting it to the Catholic position (where they differ).
There are many more example. But what it tells us is the Gospel order is
1) some "L" proto-Gospel shared as a base for Mark and Marcion/Luke
2) Marcion, adding his "Q" layer
3) Matthew using Marcion's Antithesis, as well as some "M" proto-Gospel shared with Mark
- also some of Marcion was used
4) Luke which was built on Marcion and used Matthew