Maybe I’m dense, but it appears that I have not faced all of the competitors even after beating Liadri. I am missing the challenge option on 3 of the bosses when talking to the fight manager, and just normally fighting puts me back up against Liadri. Is this a bug?
Fight manager menus and achievements panel for beating Liadri attached:
Blank Players [BDL]-Anvil Rock
Maugen Rawr- Thief/Ele
Rebalance Ideas for Thief 
