Whisper's Darkstaff

The caster conjures a 7-foot staff made of steel and shadows. This staff does 1d6 necrotic damage on hit, uses the caster's spellcasting modifier instead of Strength, but is otherwise a normal staff.

Leveling: Once the caster reaches certain levels, this spell gains additional effects:

5th level: the target must make a Constitution saving throw, taking an additional 1d6 necrotic damage on a failure.

11th level: if the target fails the Constitution saving throw, it is also stunned until the beginning of its next turn.

17th level: Instead of using the staff as a melee weapon, the caster may instead fire a globe of darkness up to 30 feet away. They must make a ranged spell attack; on hit, the target suffers 4d6 necrotic damage.