In the Snow Queen Fairy Tale version, the main boy gets Snow Queen's glass in his eyes and heart that transforms him, so that got me thinking about the new Frozen movie
So I know this could never happen bacause this is Disney, but here's a thought anyway...
Kristoff and Anna have escaped from Elsa's Ice castle but not unharmed. Elsa had used an attack that shoots glass shards that changes a person to become cruel and aggressive, Kristoff got hit while protecting Anna, Sven, and Olaf. Once they were safe, black liquid starts oozing out of Kristoff eyes from the curse taking effect. A fearful Anna swears that she will heal him from the curse, but can she when she must also break her curse?
Kristoff and Anna (c) Disney