The unique element is often the exploration of Finn's different personality in his ice form. He can be more cold - hearted in a literal sense, which creates interesting conflicts.
One popular 'Adventure Time Ice Finn Fanfic' is 'Frosty Adventures of Ice Finn'. It takes Finn in his ice form on a journey through the Ice Kingdom, facing new challenges and making strange allies.
One interesting Ice Finn fanfiction could be about his adventures in a frozen realm that wasn't shown in the original series. Maybe he discovers a new type of ice creature and has to form an alliance with it to save the day.
I really liked 'Ice Finn's Frozen Quest'. It has Ice Finn going on a journey to find a magical ice crystal that can restore balance to the Ice Kingdom. It's full of action and some really cool descriptions of the icy landscapes.
One great example could be a fanfiction where Finn and the Ice Prince have to team up to save Ooo from a new, powerful enemy. In this story, Finn's bravery and the Ice Prince's ice powers complement each other in unexpected ways. They start off as reluctant allies but gradually develop a mutual respect as they face various challenges together.
One interesting fanfiction could be where Finn and Ice King go on a journey to find a magical item that can thaw the Ice King's frozen heart in a more emotional way. Finn's sense of adventure and the Ice King's zany personality would make for a really fun and unique story.
They could also be portrayed as friends from different worlds who are trying to find common ground. The Ice Prince comes from a cold, isolated place, and Finn from a more adventurous and social world. A fanfiction could explore how they bridge this gap and create a unique bond that combines their different personalities and values.
Another option is to check out some Adventure Time fan communities on social media platforms like Reddit. There are often threads where fans share and discuss their favorite fanfictions, including those centered around Finn and Ice King. You can ask for recommendations in those communities as well.
The Fire Kingdom's Flame Princess could be an ally too. Her mastery over fire could complement Finn's powers in combat situations. Also, the various magical creatures in Ooo, like the gnomes or the fairies, could band together and support Finn. They might have their own ancient knowledge or magic that could be useful to Finn in his adventures with his godlike powers. Finn's kindness towards them in the past might make them more inclined to help him out.
Well, in fanfics regarding Finn's arm in Adventure Time, some might focus on a magical or mythical origin for his arm. For example, it could be revealed that his arm has a connection to some ancient power or being from the Land of Ooo. It could also be used as a plot device to show Finn's growth. If his arm is injured, he might have to learn to adapt and become stronger in other ways, which would be an interesting character development arc in the fanfic.