Have You Seen This Book?

Okay readers, I have a challenge for you. One that I don't hold out much hope for you solving.

Basically, there is a book from my childhood that I vaguely remember, but do not know the title or author. So, I am going to put a list of details below. If you think you know the book, let me know in the comments.

1. Set in modern day.
2. The last event in the book/series is a retelling of Ragnarok.
3. Main character is an original character.
4. Many side characters are taken from Norse mythology.
5. Loki is key, obviously, and there is a detailed description of his imprisonment.
6. It is probably from the children's fiction area (ages 8-12).
7. I owned the book about eight years ago, and I think it had been released fairly recently.
8. May also have been the last book in a series.
9. I think there is a plot point that it is all a video game, or virtual reality (this is uncertain).
10. An earlier book in the series took inspiration from the Greek Minotaur and labyrinth myth.

That's about all I remember. It isn't Percy Jackson, Ragnarok, Rune Marks, The Gospel of Loki or American Gods; before anyone suggests those.

Please if you have an inclining drop a comment below, it's really bugging me I can't remember the book.