I always had the most fun giving the parties items that were powerful but had some sort of risk or tradeoff. Something where they knew the risks, but accepted of their own free will.

Some examples for you to steal, though the numbers probably need tweaking.

Scroll of Immolation.

On reading the scroll, it is consumed and all creatures within 50' in line of effect are marked for 3d4 turns. When any such creature reaches 0 hit points, it explodes in a fiery blast and is slain. Roll their hit dice for damage. The radius is 5' for every two such hit dice, rounded up. Creatures exploded in this manner cannot be restored to life by spells that require an intact corpse.

For example, an Ogre with 8d10 hit dice will explode for 8d10 fire damage to everything within 20'.

Note that these explosions can cause explosions, and the player characters are likely marked.

(Inspired by crawl, a classic rogue like)

Helm of Debt

After receiving damage, the wearer of this helm may opt to instead receive no damage. If they do so, mark down the amount of damage that would have been taken. Keep track of damaged prevented in this manner as a running total.

The next time the bearer completes a long rest, they have two choices. They may suffer double the total damage absorbed by the helm. This damage may not be reduced or redirected. Doing so resets the total to zero.

They may instead attempt a charisma save with the DC equal to the total damage tracked. On success, no damage is taken, and the tracked damage total increases by 5.

Distance from the helm, breaking attunement, dying from other means, and similar effects do not end this process. The debt must be paid.

A creature slain while the helm's debt is unpaid is immediately sent to the hells, and may not be returned to life by conventional means.