I may be running this AP for my group and I would like to replace the one of the last fights in the last book with this homebrew unique character based on Kharn the Betrayer form Warhammer 40K. He has a unique weapon I made for him as well, a chainaxe, witch is basically a chainsaw with X3 crit. I just need to know if it is a good challenge for a possible group of 5-6 players at level 20.
They would here bits of his history throughout the adventure, but would hear it as history and legend, so they will be surprised to actually run into him.