This is set two years after Frozen ends, with Anna and Kristoff already married. Written from the perspectives of Elsa and an OC, Loki. (No, not the Asgardian.)
[Loki]
And then there were three, a trio of ice plumes rising from the ground. I was getting good at this. It was easy to let go, to release the power and the magic and the emotion, but it was near-impossible to control it. What I was doing was unthinkably difficult, the raising of perfectly crystalline cones. They were easy to make when I was angry or scared, but they scattered in random patterns that I couldn't control. I wanted to be able to plan out exactly the structures they made, to build cages and swords of ice and conquer those who had called me a trickster, a wizard, a dark warlock. Arendell was going to bow to me, that I was sure of. They loved their princess, the redheaded Anna, and respected their icy Queen Elsa. She, I had no quarrel with, but her people? They were to fall. So I closed my eyes and channeled the magic, letting the ice flow from my veins. Another spike rose, thin and deadly, spiraling into the air. Spiraling much too high.
"Stop!" I shrieked, attempting to cut off the flow of magic. It was of no use. The pillar pushed into the roof of my meager home, growing uncontrollably. I bit back a scream as it launched me into the air, rapidly propelling itself upwards. The spike that I had intended to be small and dagger like was now as large as a small mountain. So much for control.