It is impossible on a website to do justice to this saintly Pope! What shall be provided here are a few of Pope Pius XII's decrees that are not generally known or reported. He could see the forces attempting to destroy the Church and took steps to stop them in their tracks. Unfortunately he was not assisted by the prayers of the faithful sufficiently to prevent the Cardinals from defecting from the faith and presenting the Church with the Abomination of Desolation, a heretic appearing to be Pope! 
June 29, 1943 issues the Encyclcical Mystici Corporis Christi, which defines who is and is not a Catholic among many other things.
August 12,1950 issues Humani Generis which determines that Encyclicals can be infallible among many other important things.
October 11, 1954, Encyclical, Ad Caeli Reginam (Proclaiming the Queenship of Mary), Oct. 11, 1954. Establish feast for May 31.
May 1, 1955 instituted the feast of Saint Joseph the Workman on the General Calendar for May 1st.
November 16, 1955 Instituted the Restored Order of Holy Week, which also extended the Lenten fast until midnight on Holy Saturday.
