Fantasy YA novel. Read in early 2010s. Four teens go to another world (maybe though a mirror?) There’s a dragon that hypnotises people.

[Sally]

I think two of the teen were called Nathan and Beth. There was a race at the end and one of the other teens lost and was hypnotised by a dragon creature. Nathan lost the second time but avoided getting hypnotised by thinking about Beth, because he was in love with her.

[Capn]

Might it be listed here?

Fiction: Portal is Painting or Mirror:
https://www.goodreads.com/list/show/1...