Source: https://keith-baker.com/dragonmarks-thelanis-and-the-fey/
Dragon magazine ran a series called The Court of Stars that profiled Archfey, and I wrote a piece on the Prince of Frost for issue 374 (that’s him on the cover). Here’s a note from that article: “The great powers of the Feywild dance through time unburdened by its chains, leaving their marks in stories and histories. Little can be known for certain about the archfey. Some accounts say that the Maiden of the Moon was once an eladrin who rose to power through passion for the hunt. Others claim that she is a dream of the moon. Perhaps neither tale is the truth. Maybe both are. So it is with the Prince of Frost. It is foolish to seek fact in the Feywild, but one can find stories.” According to his story, the Prince of Frost was originally the Sun Prince and betrothed to one of the three Daughters of Delight. When his lover forsook him for a noble mortal warrior, his heart grew cold… and when she and her lover cast their spirits forward in time to escape him, his heart became ice. Now he waits for his love to be reborn so he can possess her; but in the meantime he takes pleasure in tormenting mortal heroes in memory of the one who stole his beloved.
The Prince of Frost is a perfectly suitable Fey to appear in Thelanis. He has long-term goals – find his beloved when she is reborn, torment mortal heroes – and he will recruit mortal agents (Greensingers, Fey Pact warlocks) to help achieve these goals. The issue is that he is defined by his story. He can’t suddenly meet a new love and drop the whole vengeance thing, or suddenly be convinced to take an interest in the war between Droaam and Breland. He is ancient and powerful, but in some ways he is simpler than most mortal villains; he is, in essence, a storybook villain. He can be subtle and clever in pursuing his goals, but at the same time, he’s going to KEEP PURSUING THOSE GOALS FOREVER until the story somehow finally comes to an end. Like the dryad, he doesn’t really learn or evolve… unless his defining story itself somehow evolves.
The next critical thing about immortal Fey is that they are bound by rules and storybook logic; this is a thing that can limit them despite their power. Most are bound to keep their promises. The Court of Stars article calls out that a player can gain concrete, mechanical benefits if they learn the true name of the Prince (and can say it); if they learn the song Lady Sharaea composed for her beloved; or if they possess the amulet the Prince of Frost gave to Sharaea. So a mortal gnome can give her word and break it a minute later; but a Ghaele is defined by her words, and can be tricked into making a promise that saves a mortal.
All of which brings us back to the question: what do they want? The answer is different for each Archfey. Most of them are simply living out their story and want whatever suits that story. The Prince of Frost wants to torment selfless heroes while searching for his beloved. The Lady of the Silver Tree wants nothing more than the care for her tree. They may be defined by feuds with other Archfey or mortals; essentially, come up with a story and it will tell you what they want.