Everywhere I've seen has said the way to unlock the mage is to turn in one of every type of mage amulet. I just went through with all 10 of them and turned them in one by one. I never left the mage quests page, I used the "turn in more amulets" button each time I turned one in. What did I do wrong?

Are you sure you don't already have him unlocked? He'll show up at the bottom of the Secret tab in the Coliseum.

It's been quite a while since I unlocked him myself, so I can't test it for you to confirm. But I seem to remember that being the requirement when I did unlock him, and I'm not sure why they would change it.

Ack you're right. I must have unlocked him before and missed the banner. Didn't realize he'd be in the secret tab!

Glad it worked out!

And yeah, all challengers that you have to unlock by doing something around the site will show up in the Secret tab, except for the Cash Shop challengers and a few of the Event challengers. The Normal tab only shows the challengers that are available for everyone by default.