Back when test realm was still around I saw lots of YouTube videos where this was discussed. How they were disappointed with what challenge mode actually is. However my take is players really don't want a challenge mode. In my personal opinion it's just players wanting to "talk tough". Now my reasoning is quite simple based on what players actually do. You will see the odd player that does some kind of challenge like Darkmoor solo, or for example Ferric who does a walk-through completely solo. Still few who make challenges for themselves.
There are so many ways to make Wizard far more challenging yet very few people actually do this. I'm sure anyone reading this can and I hope will suggest other ways to make it harder.
The very first thing that comes to mind for me is adjusting the settings so you don't know what school you are facing, or even if it is a boss. Go in blind and carrying cards like prism, because you don't know what you need.
The next thing I would suggest is if you are part of a group, don't use discord or other voice calling software. Good communication especially on cheating bosses is very useful and the ability to talk to your team is a big advantage.
Gear: now this is a big one. Players who genuinely want a challenge could play with this one. Whether using no gear, no pet or just low-level gear. This one has endless opportunities for players really wanting a challenge in wizard. For example you could just simply make sure your wizard has accuracy, so they don't fizzle, no resist, no damage.
Spells: limit what spells you use for example don't use any enchantments. Don't use attack all spells. Limit blades. Don't use feints etc etc
What would you suggest?