Of all the false prophecies I view as Antichrist seeds, The Last Roman Emperor is perhaps the most directly like the Biblical Antichrist, being defined as Greek and Roman at the same time, since it developed largely in the Byzantine Empire, it easily reconciles the way Daniel points to both Rome and Greece as the nations the Antichrist will rule. And in some of the 7th century apocalypses he's said to conquer both Syria and Egypt, which is interesting if you still think Daniel 11:40 is the Antichrist.
Usually, when dealing with these false prophecies my view is that the Antichrist figure within said Prophecy is in the role of a Decoy Antichrist. And that is certainly the case with the later elaborations of the Last Roman Emperor tradition.
But this is short, and it's attributed to a pagan Oracle. Oracles usually give cryptic prophecies, that could have two potentially opposite meanings, or an unexpected meaning that in hindsight should have been obvious. "A Prophecy that misread could have been"-Yoda, Revenge of The Sith.
So let's look at what this Prophecy says closely.
THE LATIN TIBURTINE SIBYL1. It never describes Constans as actually fighting the Antichrist, the enemy he goes to war with is Gog and Magog.
Then will arise a king of the Greeks whose name is Constans. He will be king of the Romans and the Greeks. He will be tall of stature, of handsome appearance with shining face, and well put together in all parts of his body. His reign will be ended after one hundred and twelve years. In those days there will be great riches and the earth will give fruit abundantly so that a measure of wheat will be sold for a denarius, a measure of wine for a denarius, and a measure of oil for a denarius. The king will have a text before his eyes that says: "The king of the Romans will claim the whole Christian empire for himself." He will devastate all the islands and the cities of the pagans and will destroy all idolatrous temples; he will call all pagans to baptism and in every temple the Cross of Christ will be erected. "Then Egypt and Ethiopia will be eager to stretch their hands to God." ~ Whoever does not adore the Cross of Jesus Christ will be punished by the sword. When the one hundred and twelve years have been completed, the Jews will be converted to the Lord, and "his sepulchre will be glorified by all." In those days Judah will be saved and Israel will dwell with confidence. At that time the Prince of Iniquity who will be called Antichrist will arise from the tribe of Dan. He will be the Son of Perdition, the head of pride, the master of error, the fullness of malice who will overturn the world and do wonders and great signs through dissimulation. He will delude many by magic art so that fire will seem to come down from heaven. The years will be shortened like months, the months like weeks, the weeks like days, the days like hours, and an hour like a moment. The unclean nations that Alexander, the Indian king, shut up (i.e., Gog and Magog) will arise from the North. These are the twenty-two realms whose number is like the sand of the sea. When the king of the Romans hears of this he will call his army together and vanquish and utterly destroy them. After this he will come to Jerusalem, and having put off the diadem from his head and laid aside the whole imperial garb, he will hand over the empire of the Christians to God the Father and to Jesus Christ his Son. When the Roman empire shall have ceased, then the Antichrist will be openly revealed and will sit in the House of the Lord in Jerusalem. While he is reigning, two very famous men, Elijah and Enoch, will go forth to announce the coming of the Lord. Antichrist will kill them and after three days they will be raised up by the Lord. Then there will be a great persecution, such as has not been before nor shall be thereafter. The Lord will shorten those days for the sake of the elect, and the Antichrist will be slain by the power of God through Michael the Archangel on the Mount of Olives.
Translated from the edition of E. Sackur, Sibyllinische Texte und Forschungen. pp. 185—86.
2. Although the Antichrist is mentioned while Constans is still reigning, it's not till after Constans puts down his Crown in Jerusalem that the Antichrist is openly revealed, and reigns in the House of God in Jerusalem. Same place we were just told Constans was.
I think this prophecy, even as it's author originally intended, is open to a reading where Constans and The Antichrist are the same individual. That he will "give up" his authority to beings that present themselves as being God and Jesus but are perhaps actually Satan and The False Prophet.
Constans is an interesting name, it's a diminutive form of Constantine and Constantinius (but a few lesser known Emperors went by that name exactly). The seventh century Syrian elaborations on the Last Roman Emperor figure didn't give him a name. And the Western Catholic tradition of the Great Catholic Monarch removed the Greek affiliation altogether saying he'll descend from Clovis, the Merovingian. However...
When Constantinople fell to the Turks in 1453 AD. Emperor Constantine XI removed his royal garments on the battlefield when he knew it was lost so no one could tell who he was. After the battle was over the Turks identified a body as his and marched it around the city in victory, but the people failed to recognize it as Constantine. No body was ever indisputably identified as Constantine. A rumor spread that an Angel had saved him and turned him into a marble statue and hid him beneath the wall of Constantinople, and that one day God would revive him to drive out the Turks. The legacy of this legend remained important to the Greeks ever since, it was rekindled during their War of Independence in the 1800s and lingers to this day.
You may be thinking of course, "How can the same person be both King of the Greeks and a Prince from the Tribe of Dan?"
Ezekiel 27 speaks of Dan and Javan having a connection. And indeed Greek mythology speaks of the Danoi. This further leads to speculation about connecting Dan to the Tutha de Dannan who in Irish mythology came from Northern Europe. I'm highly skeptical of most British Israelism claims, but the Tribe of Dan is very interesting.
Britam identifies Dan with Denmark (which is the only Britam identification I kinda agree with). The Royal family of modern Greece from George I on are also Danish Royalty by virtue of their direct Pater-lineal descent from Christian IX of Denmark. Every modern King of Greece (King of the Hellenes as they call themselves) is also officially a Prince of Denmark. King of the Greeks and Prince of Dan.
I discus the genealogy of George I of Greece and Christian IX of Denmark on a different blog. That information can be overlapped with my Genealogy of The Antichrist study to show that they descend from the Seleucid Dynasty. as well as probable Merovingian descent from Clovis. This family is also taking over the British Royal family, involving a few of the lines different people have in different ways sought to connect to the House of David.
The current King in exile is Constantine II and is often called by his supporters Constantine XIII, viewing the modern Greek Kingdom as heir to the Byzantine Empire, and evoking the mythology about Constantine XI.
Constantine II has 4 children, Pavolos the oldest son is the Crown-Prince. Pavolos has 5 children, 4 of whom were born in the United States. Princess Maria-Olympia, Prince Constantine-Alexios, and Prince Achileas-Andreas all three of whom were born in New York. Prince Odysseus-Kimon and Prince Aristidis-Stravos who was born in Los Angeles.
The pieces are in place for some charismatic leader of this royal family to bring together the Byzantine Last Roman Emperor tradition, the Great Catholic Monarch Tradition, and the British Israelite understanding of Messiah Ben-Joseph and/or the Talmudic tradition that says Messiah Ben-David will also be half Danite, like how Samson was half Danite and half Judean.
Modern Greece had 7 Kings when it was a Kingdom. Now that is certainly not what the 7 Kings of Revelation mainly mean as I've firmly shown elsewhere, but it's interesting how patterns repeat.
Long ago when I hadn't settled on my current view of the 7 heads, when discussing a possible connection to the Kings of Rome, I argued that the 7th reigning a little while might not be about reign length so much as implying being driven from his position rather then reigning till he died as a King normally does. Which also happened to Constantine II.
From there it is interesting that it was during the reign of the Sixth King that Israel was reestablished in 1948.
Update Feb21st2016: Another option I just considered re-reading the Oracle is maybe the "Antichrist" there is really The False Prophet.