I just managed to unlock Redeemer Fanatic tonight. I used Legacy, Team Leader Tachyon, Visionary, Omnitron-X, and Fanatic. They fought in the Freedom Tower Environment.
Thanks, all, for the suggestions. I owe my success to this forum community. Mr. Fixer ended up being too effective with Jack Handle and Riveting Crane, which enabled him to kill off Apostate too quickly before Fanatic could get all the requisite cards in play and then deal the final stroke, so I ended up benching him for not being a good team player. ;-)
Otherwise, yes, he'd normally be awesome and would make a fight against Apostate much easier.
Prime Warden and Dark Watch unlocks await me further, but for now it's a great sigh of relief I'm feeling. Thank you all, again.