전우치전

This is folktale about a man capable of perfoming Taoist magic. He also has kind of a Robinhood spirit, which makes reading this very enjoyable! Each chapter is 4-6 pages long, and they're mostly independant (there is a continuing storyline, but each chapter focuses on one event/encounter), which is great for language learners.

Since this is a darakwon graded reader, there's also some vocab under each page, along with some additional vocab, grammar, and culture notes as bubbles within the text. These are very well chosen for a B2 graded reader.

For the vocab difficulty, there are probably a bunch of words in here that you wouldn't find in children's books around the same level. Most of those harder words (i.e. 조선 시대 related vocab, more complex expressions...) are in the vocab notes however. I would recommend, if you can, to read 춘향전 (the other B2 darakwon graded reader) first. I feel like the grammar in that one is slightly easier, and since they have some common vocab, it makes reading this one easier. For the grammar difficulty, you can expect some sentences that can be rather long, with a combination of several grammar points used. You'll get used to grammar points where one part is dropped as well, like -아/어(서), -니(까), -다(가), -자(마자)... Here are a couple grammar points you'll come across in this, to give a better idea of the level: ㄹ 통해서, (으)려면, ㄴ 척하다, 어아 버리다, 법이다, ㄴ 덕분에...

(전우치전's vocab might also be slightly easier than 춘향전's, but I'm honestly not sure whether that's actually the case or if it's just an impression due to the order that I read them in.)