Firstly, what is terror? I prefer to define terror as the "opposite of hope," a condition that stems from lack of trust that God loves you and wills what's best for you.
In her Diary, St. Faustina writes of terror - the terror of dying souls as well as her own brief moments of terror. In one instance, Jesus asks her to help Him to save souls by praying the Chaplet of Divine Mercy for dying sinners. She records, "I found myself in a strange cottage where an elderly man was dying amidst great torments. All about the bed was a multitude of demons and the family, who were crying. When I began to pray, the spirits of darkness fled, with hissing and threats directed at me. The soul became calm and, filled with trust, rested in the Lord" (1798).
The demons knew they didn't stand a chance against St. Faustina and the Chaplet.
Yet St. Faustina, too, experienced moments of terror. Jesus rebukes her for this at one point, saying:
I am displeased when a soul yields to vain terrors. Who will dare to touch you when you are with Me? Most dear to Me is the soul that strongly believes in My goodness and has complete trust in Me (453).
Saint Faustina would eventually learn to whom she can turn in order to allay her fears and unite her to Jesus. It was none other than Jesus' foster father, St. Joseph. The famous Litany of St. Joseph identifies him under the title Terror of Demons, and it's no wonder. Surely, this man entrusted by God with the singular mission of caring for and protecting the Holy Family was endowed with graces enough to strike fear in the forces of darkness. The demons don't stand a chance against St. Joseph. Saint Faustina writes:
Saint Joseph urged me to have a constant devotion to him. ... He has promised me this special help and protection (1203).
When you find yourself feeling overcome by the trials of life, turn to St. Joseph. He was a man who, in his earthly life, never succumbed to "vain terrors." He remained ever grounded in faith, ever attuned to the will of God in his life. From Heaven, he stands as a go-to saint to help you when forces beyond your control - including demonic forces - seek to unsettle you and pull you toward despair and ruin.
At the end of our lives, many people are susceptible to despair. Saint Joseph, Terror of Demons, will squash such despair and all things that stand in opposition to the hope found in the Risen Christ. From Heaven, this humble, quiet man of strength will lead us to the peace found in Jesus.
Saint Joseph, Terror of Demons, protect us.