What is the comparison between roman catholic and Iglesia ni cristo and mormonism?

All three are "Christian" religions

Catholics believe in the Trinity, LDS and INC churches do not.

Catholic and LDS churches see Christ as a God (although in very different ways). INC does not see Christ as a God, but as a mediator between man and God the Father.

The Catholic church professes to be the same continuous church that Christ founded while he was on the earth. LDS and INC churches believe that the church Christ founded fell into apostasy after the death of the apostles, and therefore profess to be a restoration of the church Christ founded while he was on the earth.

According to each sect: The Catholic church has a Pope, who has the authority of God, passed all the way down from Peter. The INC was restored by a Prophet (Felix Manolo) with the authority of god, but he was the last that will be seen on the earth. The LDS Church claims to have been restored by a Prophet as well, but claims that the authority of God carried by that man (Joseph Smith Jr) has been passed down (similar to Catholic authority) and that the Church today is still led by a living prophet and twelve apostles.

There are plenty more things to compare. These are the biggest (imho).