Maybe a magic weapon that could be like the golden shower,Giving a debuff something like that. I could also suggest some ranger boomerang-y items for Hardmode as there are only a few HM boomerangs.Perhaps a pirate army type boomerang that would be the Steering wheel maybe?I was having trouble coming up with something for mage if you couldn't already notice I was thinking about a pre-HM to early HM weapon that fires all of the different staff projectiles randomly. Also a weapon that fires magical spikes could works, it would by default explode into fragments. Just a couple ideas i've been debating
Also you could add a magic weapons that shoots friendly and enemy players like a cleric which could add some interesting elements to the mage.
Maybe a steampunk item that shoots razor sharp blades or maybe gears/cogs?
Just a few ideas that came to mind as I wrote this