What's the Name of That Book??? discussion

This topic is about
The Legend of Nightfall
SOLVED: Adult Fiction
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Fantasy Novel Hero is a rogue who can change how much he weighs magically - villain has ice powers [s]
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In the book, the hero is a rogue who could change his weight magically. In one instance he races horses and makes himself weigh alot at the scales to create a handicap, then makes himself as light as possible during the race to give his horse an edge. In another, he becomes lightweight when falling from the palace and floats down like a feather (near the end I believe). The hero is also a rogue who is very good with throwing daggers I think.
The villain was somehow tied to the royalty in some sort of manipulative advisor role, and also had a magical power. It had something to do with ice as he was able to freeze a swamp over to walk on it when in pursuit of the hero at some point.
I think the magical powers may have been called knacks, but I may be wrong.
This book has been eluding me for over a decade, and I can't remember any details that are googleable, so I hope this helps end the mystery!
Thanks for your time.
Cheers
bg