Christ redeemed us from the curse of the Law by being cursed for our sake — Gal 3:13
St. Paul calls the Law a curse because its primary purpose to reveal to us our sin — our separation from God. No mere human being is capabe of fulfilling the Law, because we all sin. When compared to the Law, our lives are all a sinful mess. Even the greatest of us are cursed by the Law because they, too, sin. Thus, when we see ourselves and all of humanity from the perspective of the Law, it becomes very clear that we are incapable of saving ourselves — we need God, because only God can save.
In a fantasy setting, there can be any number of things that are constant reminders of the distance between fallen humanity and God. These coud be physical monuments that dot the landscape, they could be progressive mutations that are manifestations of sin, they could be monsters that are born of sins humans commit, etc. The underlying point is that sans God, humanity is cursed and that God has revealed this through the Law (or its fantasy analogy).
Therefore the Lord Himself eill give you a sign. Look, the virgin is with child and shall bear a son, and shall name him Emmanuel (God is With Us) — Isaiah 7:14
For the purposes of building a fantasy word, one only need to understand prophesy in terms of Christ. The OT actually tells us more about Christ than does the NT. Thus, prophesy can be hinted at with no real details (unless you feel so inclined) because they all predict Christ.
The Pre-Incarnate Christ
Then King Nabuchadnezzar was astonised and rose up quickly. He said to his counselors, "Was it not three men that we threw bound into the fire?" They answered the king, "True, O King." He replied, "But I see four men unbound, walking in the middle of the fire, and they ar not hurt; and the fourth has the appearnace of a god." — Daniel 3:24-25
There are several instances in the OT when a divine figure like that in Daniel 3:35, often call the Angel of the Lord, who the Fathers of the Church understand to be the Son of God before He became incarnate. In may cases, He prefigures the salvific action of the Incarnation, such as saving Shadrach, Meshach and Abednego from the fire.
In a fantasy setting, there can be a few flavor stories about the Angel of the Lord — the pre-Incarnate Christ — making dramatic appearances to save people who are faithful to God prior to the Incarnation.
Types of Christ
Whenever Moses held up his hand, Israel prevailed. But Moses' hands grew weary; so they took a stone and put it under him, and he sat on it. Aaron and Hur held up his hands, one on one side, and the other on the other side; so his hands were steady until the sun set. And Joshua defeated Amalek and his people — Exodus 17:11-13
Throughout the OT there are people and things that prefigure Christ. The most obvious of these is Moses. His upbringing as an Egyptian and his self-imposed exile made Moses an Other — though he was a Hebrew by heritage, he never lived among them. Despite this, he went to his people as a Hebrew to save them from slavery. God finally freed them by having death passover their households — marked with a cross of blood. Christ came to us as a human being, despite being the radical Other — God. He saves us from the slavery to sin and death by being crucified on a cross so that death is destroyed by death — it will pass over us.
In the above quote, Moses prefigures the crucifixion. The saving action of having his hands lifted is accomplished in cruciform by having Aaron and Hur hold up His hands. King David is annointed (oil poured over his head) as King. Christ and Messiah mean "the Annointed One."
For the sake of a fantasy setting, there can be any number of people who prefigure the Christ — the story can be as simple as the quote above. Someone secures victory over the forces of evil by an action that suggests the means of torture and death suffered by the Christ.