NAF – New artifacts with unique properties.

They do have an effect, but I would like a stronger and more targeted effect, for example, +50, +100 mana.

What about some kind of artifact that you can wear and, say, every three days, get 50 mana, like a portable well... That would be interesting.
You could even make it like a one-time-use potion. It's in your backpack, you put it on – the artifact is destroyed, and you get the bonus. But you need to make it so that the artifact can't be equipped when you pick it up on the map.