St. Louis de Montfort writes in True Devotion to Mary:
"God has never made and formed but one enmity; but it is an irreconcilable one, which shall endure and grow even to the end. It is between Mary, His worthy Mother, and the devil -- between the children and servants of the Blessed Virgin, and the children and tools of Lucifer.
“The most terrible of all the enemies which God has set up against the devil is His Holy Mother Mary... the humble Mary will always have the victory over that proud spirit, and so great a victory that she will go so far as to crush his head, where his pride dwells.”
St. Alphonsus of Liguori adds:
“Still more was it becoming that God should preserve her from original sin, for he destined her to crush the head of that infernal serpent, which, by seducing our first parents, entailed death upon all men: and this our Lord foretold: I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head.”
St. Maximilian Kolbe tells us:
“There is much evil in the world, but let us not forget the Immaculate is more powerful yet, and that she will crush the infernal serpent's head.”
Pope Saint Pius X:
“Let the storm rage and the sky darken -- not for that shall we be dismayed. If we trust as we should in Mary, we shall recognize in her, the Virgin Most Powerful ‘who with virginal foot did crush the head of the serpent’”.
Our Lady at Fatima in 1917:
“In the end, my Immaculate Heart will triumph.”