Early Christians initiated converts in March and April by baptism. Mithraism initiated their new members at this time as well.
Early Christians were naked when they were baptized. After immersion, they then put on white clothing and a crown. They carried a candle and walked in a procession to a basilica. Followers of Mithra were also baptized naked, put on white clothing and a crown, and walked in a procession to the temple. However, they carried torches.
At Pentecost, the followers of Jesus were recorded as speaking in tongues. At Trophonius and Delos, the Pagan priestesses also spoke in tongues: They appeared to speak in such a way that each person present heard her words in the observer's own language.
An inscription to Mithras reads: "He who will not eat of my body and drink of my blood, so that he will be made on with me and I with him, the same shall not know salvation." 1 In John 6:53-54, Jesus is said to have repeated this theme: "...Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you. Whoso eateth my flesh, and drinketh my blood, hath eternal life; and I will raise him up at the last day." (KJV)
The Bible records that Jesus was crucified between two thieves. One went to heaven and the other to hell. In the Mithras mysteries, a common image showed Mithras flanked by two torchbearers, one on either side. One held a torch pointed upwards, the other downwards. This symbolized ascent to heaven or descent to hell.
In Attis, a bull was slaughtered while on a perforated platform. The animal's blood flowed down over an initiate who stood in a pit under the platform. The believer was then considered to have been "born again." Poor people could only afford a sheep, and so were literally washed in the blood of the lamb. This practice was interpreted symbolically by Christians.
There were many additional points of similarity between Mithraism and Christianity. 2 St. Augustine even declared that the priests of Mithraism worshiped the same God as he did: Followers of both religions celebrated a ritual meal involving bread. It was called a missa in Latin or mass in English.
Both the Catholic church and Mithraism had a total of seven sacraments.
Epiphany, JAN-6, was originally the festival in which the followers of Mithra celebrated the visit of the Magi to their newborn god-man. The Christian Church took it over in the 9th century.
This along with many other things leads me to search for anything in Christianity that may be considered unique to Christianity.