Young Adult Fantasy is perhaps most easily defined by the age range of the audience it is written for (12-18ish). This particular definition means that the sub-genre is wide open and can borrow tropes and ideas from any other sub-genre.
YA Fantasy does have common themes and tropes. Obviously, coming of age stories are very common—the protagonist tends to have a similar age as readers and goes through some kind of transformation. Younger protagonists have a strong capacity for change and transformation. The trope of transformation is powerful in Fantasy, and especially so in YA.
YA also has emotional potency—either of new love, of family, of fear, of any other emotion. A big reason for the emotional potency of YA Fantasy is the featuring of first experiences. Any first experience is new, fresh, poignant, and this with an emotional potency draws readers (of all ages) into its world.
Variable. YA Fantasy can be found across all types of sub-genres, so magic may be a huge component to the story, or it may not.
Variable. YA Fantasy sometimes has a bad reputation for its shallowness. Indeed, some books in this sub-genre lack depth, but others are surprisingly complex.
Moderate to High. At the very least, the protagonist of YA stories is well developed. But, the best YA stories have a cast of characters, all of whom have strong characterization. Characterization is important to the development of emotional potency and that ever present theme, coming of age.
High. YA novels are rarely experimental when it comes to how a story is told and so plots are significant to moving the story forward and pushing for transformation.
Variable—but generally not super graphic.
All! YA Fantasy is mostly defined by the age of its targeted audience, but it can be a story of High Fantasy, of vampires, of Mythic Fantasy, of Dystopias, of Portal Fantasy, of anything really. Coming of Age is a subgenre that's also heavily featured in many YA Fantasy tales.
By J.K. Rowling. An incredibly popular and renowned series about Harry Potter, who at the at age of eleven finds out he's a wizard and so begins his heroic journey to save the secret wizarding world and our own from a certain dark wizard.
By C.S. Lewis. This classic series is part of the High Fantasy sub-genre and features young protagonists that can move between our world and the magical world of Narnia.
By Philip Pullman. An epic series that follows the coming-of-age stories of two protagonists that wander through parallel universes.This series addresses a wide range of ideas: physics, philosophy, theology, tragedy.
By Rick Riordan. The series begins with the revelation that Percy is actually the son of Poseidon. Adventure on the scale of Greek myth ensues.
By Jonathan Stroud. This series follows a magician in training and Bartimaeus, a 5,000 year old djinni (who has quite the wit).
By Stephenie Meyer. A series about love, high school romances, vampires, werewolves, and supernatural powers. This series has a specific audience of teenage girls.
By T.H. White. An Arthurian retelling and is also very much a coming of age story.
By Veronica Roth. The world of this novel is dystopian. Its theme is of adolescent anxiety, specifically that coming of age means moving on and sometimes leaving behind those you love.
By Robin McKinley. A classic book that features many recognizable Fantasy tropes: royalty, romance, enchantment, dragons, war.
By Jodi Meadows. A book with an original story: in the land of Range the same million souls are reborn again and again, until one day the first new soul in a thousand years appears.