I can't get challenged by Jaxon no matter how many times I clicked. I know he was still alive since my roomate was still fighting him. why is this? and will I miss out on the achievement?

maybe you need to click Jaxon and Ian too? There may be a piece of dialog you need first. Also, try to disable extensions one by one or clear out your cache etc your browser.

tried that, unfortunately it won't work :C

Sometimes a hard refresh is necessary, I had that problem with the locked room. Randomly click? Change browser? Fille a Ticket and hope they get to you in time.

Did you check the BC to see if Twisted Jaxon was there as an opponent? Maybe just the popup event to tell you were challenged didn't work.