It's Sunday, I performed some minor home repairs, I got to talk with my son, there's a rye and coke on ice, and I'm feeling creative.
A Facebook post asked about a magical item for an 'artificer artillerist.' That smacks of 5e, but I am firmly entrenched in the idea that all permanent magical items should have some form of drawback.
Still, I thought of this, the Dragonseye Amulet.
The Dragonseye Amulet is noted for its potency, as it allows its wielder to channel primal chaos and draconic magic into their own castings, resulting in spells of greater power than normally possible. Legends say that while it increases the power of spells, channeling this eldritch primordial power leaves its user drained and exhausted - sometimes fatally so.
After all, the Dragonseye Amulet is how Gyges the Faithless leveled the city of Sarnath, La Voisin the Red annihilated the Army of Abramelin, and how Hudolf Ress the Fool brought the caverns of Nemetorszag down upon his head (and the heads of his companions and the combined might of several Underdark kingdoms). He and his companions were widely known as fools throughout the multiverse, so it was both a fitting and expected end - it being a useful end was entirely accidental.
Mechanically, this item adds 3d4 dice to whatever spell is cast; the downside being the same amount of temporary Constitution damage is dealt to the user, which can mean possible death. In my games, at least, this roll is subject to our cascading (or exploding) dice rules, meaning that it can get out of hand quickly.
For example, say your Fireball normally does 6d6 damage. Utilizing the Dragonseye Amulet lets you roll 3d4 and add that many d6 dice to the damage, which sounds great until the caster using it collapses unconscious.
In addition, in games (like 5e) that care about exhaustion, using the Dragonseye Amulet gives its user two levels of exhaustion.
Of course, variations abound - half the dice in Con damage and one level of exhaustion may be more than enough to save this device for only the most difficult situations.
Moral of the story - don't ever use Constitution as a dump stat.