I guess you haven't traced the thread back very far, but for brevity, I'll detail a few. The Immaculate Conception, praying to saints and to Mary, Infallibility of the Pope (not to mention the whole idea of a Pope), Purgatory. Those are the main ones.
My authority? The Word of God, as written in the Holy Bible. The Word is the final, ultimate, and only true authority.
I know because I can read, and I don't need someone to interpret what I'm reading. I also have reference materials available to look up the original Greek and Hebrew words, plus, I pray and ask God to show me the Truth, and I'm bold enough to believe that He answers my prayers. I am not blinded by Tradition, unlike some others here, and I don't blindly follow Tradition when I see something in the Word that contradicts it.
The RCC is NOT infallible, it is guilty of gross distortion of truth and has reversed itself on various matters several times. History is replete with the abuses of the RCC, i.e. the Inquisition, the Crusades, their inattention to the Jews during WWII, and their tolerance of apostate Popes. Not a pretty picture at all.