Certain Orthodox Christian clergy and laymen infected with the demonically-influenced super heresy of Ecumenism  attempt to discredit and slander the Holy Fathers by saying the Monophysites (non-Chalcedonians) had taught the exact Christology the Orthodox Christians taught at the Fourth Ecumenical Council. Consequently, such individuals fail to recognize that by this logic they are simultaneously making the following erroneous claims:
1) That the Church through its Fourth Ecumenical Council and Holy Fathers erred in anathematizing the Monophysites. What this then leads one to believe is that the 4th Ecumenical Council is not truly an Ecumenical Council but a pseudo-council, and the Holy Fathers were not truly illumined God-bearing Fathers led by the Spirit of Truth but were pseudo-fathers the Church has erroneously canonized and venerated over the centuries.
2) That because the Church supposedly fell into error by anathematizing the Monophysites at the 4th Ecumenical Council, Jesus Christ should be deemed a liar and not the God-Man when He said the Gates of Hades would not prevail against the Church (Mt. 16:16-18) and when He promised Spirit of Truth to guide the Church into all the truth (Jn. 16:13).
3) That the miraculous revelation of St. Euphemia the Great Martyr to be demonic and false .
4) That because the Monophysite confession supposedly was the same confession as the Orthodox, and that the Orthodox simply misunderstood the Monophysite's which led to the supposedly erroneous anathema, the Monophysites have always been members of the Orthodox Church, though this reality supposedly has not been so visible over time because of certain prejudices, narrow-mindedness, over-zealotry, and ultra-conservative tendencies. This then leads certain Orthodox clergy and laymen to practice Common Prayer services with the Monophysites, and even commune Monophysites in their Orthodox parishes, and by extension, Orthodox clergy and laymen to "commune" in Monophysite parishes.
St. Paisios the Athonite, whom we commemorate on July 12, had much to say about Ecumenism, Common Prayer with the heterodox, the invalidity of heterodox "mysteries", and the erroneous Ecumenist's phronema concerning the Monophysites, which we read of down below.
 After St. Ephraim of Katounakia’s divine revelation, he stated “Ecumenism is dominated by unclean spirits.” Likewise, St. Gabriel of Georgia the Fool for Christ says, “Ecumenism is a super heresy.” See “Elder Ephraim of Katounakia, Holy Mountain: Ecumenism is Dominated by Unclean Spirits,” impantokratoros.gr, https://www.impantokratoros.gr/C54EBF09.en.aspx?__cf_chl_jschl_tk__=85604d57dc8d638502fffa3f3def9e4fecd641b5-1615935784-0-AaqW_unwnDE2wx599T4ySJBPKTcxde4PHTO-pFe0eTo2eFVoXRnjso_xRUTviMN5U9wdLk4YKqjFjsVbKlxhcpnockf7oua_sVqFsmXk32Xj5iPboBkrrLWIcu3CjMw8TGHS_eOIDdK-uH0rVzTfjRs0UBm8mVYkrKRKn1kFZ8MIZV29I31OAFLARaC-6m9lSrhjk2mhKo2qUKxxoiQ9MD3AtE4z8mQ5DqSRzJoJbpLQvs6sz-5ia3sR32-2Lqo2g4pqgKP9JMd2eishHK6vXVGqAgi4GaiTGgkdrXuNKcsFG9FSJpUskE6a6GJCXtkW_-fcjy3gJK4jrgy-ml9cSR0yXh-NJWJiIrSIL-JreTcDKgNZ9A401a2rjTMT9Luaf_vbZrnEaSyqrDYqvZ6gwrA citing Holy and Great Synod of the Orthodox Church - A Synod Lacking in Synodicity and Orthodox Self-Awareness (Trikala: Synaxis of Orthodox Romaics “Fotis Kontoglou,” 2016), https://www.impantokratoros.gr/C54EBF09.en.aspx. See also “Edifications,” monkgabriel.ge, Edifications - St. Gabriel Confessor and Fool for Christ's Sake (monkgabriel.ge). See also “False Ecumenism Archives,” orthodoxchurchquotes.com, False Ecumenism Archives - Orthodox Church Quotes.
 You can read of the miraculous revelation of St. Euphemia the Great Martyr proving the Monophysite confession to be heretical and opposed to the Orthodox confession at the 4th Ecumenical Council here: The Miracle of Saint Euphemia the All-Praised / OrthoChristian.Com.
“Today unfortunately, the European courtesy has come in and they try to show themselves as being nice. They wish to show superiority and finally they end up worshiping the two horned devil. “One religion, they tell you, should exist” and they level out everything. Some also come to me and tell me, “All of us who believe in Christ should create one religion.” Now it is as if you are telling me, I told them, about gold and copper, so many carats of gold and that much copper, that was separated, to gather them and make them one again. Is it correct to mix them again? Ask a jeweler. Is it proper to mix trash with gold? So much struggle was waged to distil the dogma. The Holy Fathers must have known something for prohibiting the relationships with the heretics. Today they say: “We should pray together not only with the heretics but also with the Buddhist and with the fire worshiper and the demon worshiper. The Orthodox must also be present in common prayers and in their conferences. It is a presence.” What presence? They resolve everything with logic and justify the unjustifiable. The European mind also believes that spiritual matters can also come into the Common Market. Some of the Orthodox who are shallow and wish to make a promotion, “a mission,” they arrange conferences with the heterodox to cause a sensation, believing this way that they promote Orthodoxy, by becoming so to speak “Hungarian goulash” with the false believers. Then the super-zealots take hold of the other end; they also blaspheme against the Mysteries of the New-calendarists, etc. and deeply scandalize the souls who have piety and Orthodox sensitivity. On the other hand, the heterodox come to conferences, act like teachers, take whatever good spiritual thing they find from the Orthodox, they process it, they give it their own color and mark and they present it as a prototype. And the strange contemporary world becomes touched by such strange things and is spiritually destroyed. The Lord though at the appropriate time will present the Marks, the Eugenikos and the Gregory Palamas’ who will assemble all our deeply scandalized brothers, to confess the Orthodox faith and strengthen the traditions of the Church and give great joy to our Mother, the Church.”
"They resolve everything with logic and justify the unjustifiable."
“He [St. Paisios] particularly respected the Ecumenical throne. He recognized its pan-orthodox mission and understood the difficult position it was in. He prayed a lot and publicly defended it during many instances. As a mouthpiece we witnessed the Elder to be a strong fighter against the heretics. On matters of faith he was precise and uncompromising. He had a great Orthodox sensitivity and for this he would not accept common prayers and communion with non Orthodox persons. He would stress: "For us to pray together with somebody, we must agree on the faith". He would break his relationship or avoid meeting clerics who participated in common prayers with the heterodox. The "mysteries" of the heterodox he would not recognize and he would advise that those who were coming over to the Orthodox Church be properly catechized before baptism. He fought intensely against ecumenism and would talk about the greatness and uniqueness of Orthodoxy, information which derived from his heart that was full of divine grace. His life indicated the superiority of Orthodoxy. For a period he stopped, together with almost the rest of the Holy Mountain, to commemorate the patriarch Athenagoras for his dangerous openings to the Roman Catholics. But he would do so with anguish. "I pray" he would say to someone, "so that God cut some days off my life and give them to the patriarch Athenagoras to complete his repentance". About the Anti-chalcedonians (monophysites) he would say: "They [Ecumenists] do not say that they [the Monophysites] did not understand the Holy Fathers but that the Holy Fathers did not understand them [the Monophysites]. Namely, as if they [the Monophysites] are right and were misunderstood [by the Holy Fathers]". He characterized as blasphemy against the Holy Fathers the proposed cleansing of the Liturgical books from the characterizations of the heretics Dioscorus and Sevirus. He said [concerning the Ecuenist mindset], "So many Holy Fathers who had divine illumination and were their contemporaries, [supposedly] did not understand them [the Monophysites] but misunderstood them, and here we come so many centuries later to correct the Holy Fathers? Why don't they even consider the miracle of Saint Euphimia? Is it possible that even she had misunderstood the book of the heretics?" Without seeking to appear as [a] confessor, with his ways, he would react, talk and write to ecclesiastic people. "The church" he would say "is not a boat of every bishop to do what he pleases". His reactions were followed by a lot of prayer and love for the Church but also for those who deviated and by assumed apathy, distinction and greater enlightenment.”
"On matters of faith he was precise and uncompromising. He had a great Orthodox sensitivity and for this he would not accept common prayers and communion with non Orthodox persons."
“He considered the Anti-Chalcedonians (that is, the Monophysites [Oriental Orthodox])—along with the other heretics and those of other religions—to be creatures of God and our brothers according to the flesh, in terms of our common descent from Adam; but he did not consider them children of God and our brothers according to the spirit, characterizations he believed applied only to Orthodox Christians. Regarding the Monophysites’ sympathizers and their fervent supporters among the Orthodox, he observed, “They don’t say that the Monophysites didn’t understand the Holy Fathers—they say that the Holy Fathers didn’t understand them. In other words, they talk as if they’re right, and the Fathers misunderstood them.” He considered proposals to erase from the liturgical books statements identifying Dioscorus and Severus as heretics to be a blasphemy against the Holy Fathers. He said, “So many divinely enlightened Holy Fathers who were there at the time didn’t understand them, took them the wrong way, and now we come along after so many centuries to correct the Holy Fathers? And they don’t take the miracle of Saint Euphemia into account? Did she misunderstand the heretics’ tome too?” Without trying to seem like a confessor of the faith, the elder, in his own way, expressed his opposition regarding various matters, speaking to and writing ecclesiastical figures. “The Church,” he would say, “isn’t the ship of each bishop to do with as he pleases.” These reactions of his were accompanied by much prayer and love, not only for the Church, but also for those who were deviating from the faith; and all was the fruit of dispassion, discernment, and enlightenment from above. The Fourth Ecumenical Council was held in Chalcedon in 451. The Council taught that Jesus Christ had two natures, divine and human. Those who rejected this teaching became known as Monophysites, from the Greek words for “single nature.” The Council decided in favor of the dogma of two natures in Christ, and it condemned those who rejected its authority and persisted in their errors, expelling them from the Body of Christ. The various communions descended from those who rejected the Council have been known by a variety of names, including Monophysites, Non-Chalcedonians, the “Lesser” or “Separated” Eastern Churches, Copts, and Jacobites; and in latter times by other names, including Miaphysites, Henophysites, Pre-Chalcedonians, and Oriental Orthodox. The conclusions of the Fourth Council were affirmed at the Fifth, Sixth, and Seventh Ecumenical Councils, and the Fathers of the Council are celebrated yearly on the Sunday between July 13 and 19. The elder refers to the claim among supporters of union with the Non-Chalcedonians that the disagreement at the Fourth Ecumenical Council was essentially a tragic misunderstanding, the Holy Fathers there present failing to consider that people of differing backgrounds sometimes use different words to refer to the same thing. Dioscorus was among the leaders of the anti-Orthodox at the Fourth Council, and Severus was one of the Council’s most fervent critics. Both are regarded as saints by Non-Chalcedonians (Monophysites). The Church’s liturgical texts, however, speak of the Fourth Council’s victory over heresy, some specifically identifying Dioscorus and Severus as enemies of the Faith. A union of the sort the elder rejected would require all these references to be deleted; and, in general, a rewriting of liturgical texts, saints’ lives, and educational literature touching on the Fourth Council. The Church at which the Fourth Council met housed the relics of Saint Euphemia, and, after prolonged discussion failed to produce an agreement, it was decided to place each party’s confession of faith (or “tome”) in her tomb and supplicate God to reveal His will in the matter through His Saint. The imperial seal was set on the tomb and a guard appointed, and those present spent days in fasting and prayer. When the tomb was opened in the presence of all, the tome of the Orthodox was found in the saint’s right hand, while that of Dioscorus and his party was at her feet. This miracle is commemorated by the Church on July 11: “O Euphimia,” reads one hymn, “Christ’s comely virgin, thou didst fill the Orthodox with gladness and didst cover with shame all the heretics; for at the holy Fourth Council in Chalcedon, thou didst confirm what the Fathers decreed aright” (Great Horologion, p. 541).”
“So many divinely enlightened Holy Fathers who were there at the time didn’t understand them, took them the wrong way, and now we come along after so many centuries to correct the Holy Fathers? And they don’t take the miracle of Saint Euphemia into account? Did she misunderstand the heretics’ tome too?”
Apolytikion of St. Euphemia the Great Martyr:
O Euphemia, thou didst gladden the Orthodox, and put the heretics to shame. Thou didst confirm the Fathers' teaching at the Fourth Council. O glorious Martyr, entreat Christ our God to grant us His great mercy.