A great game with a lot of interesting ideas for loot and magic is Legend of Dungeon, though you don't have mana and only get magic tomes that you can use. The tomes do all kinds of things, but you never know what they're going to do until you test them. It may be magic missile, lights, or summon an ally, or summon a dangerous enemy, or summon random things like cats, crates, and stone blocks.
Basically, magic in my opinion should be quirky and strange. It should impact the game in ways like that fundamentally change the environment. Like making tiny storm clouds that are hard to see through. Or filling a room with water. Or inverting gravity.