I wrote up Ranna below in a somewhat balanced version that isn't able to be freely cast at-will and tried to include some downside for the bell ringer. The downside is pretty minimal at higher levels but still has a risk when at low hp.
Ranna, the Sleeper - The high-pitched tinkling of this bell brings silence in its wake.
Wonderous item, Legendary
This bell has Charges equal to half your character level (minimum 1). While holding it, you can use an action to ring the bell and expend 1 or more of its Charges to cast the Sleep spell at 2nd-level on all creatures that can hear it within 30 feet. You can increase the spell slot level by one for each additional charge you expend.
Before casting the spell, make a DC 14 Charisma (Performance) check. On a successful check, you are immune to the effects of the spell while resolving the effects of the spell. On a failed check, resolve the effects of the spell.
The bell regains 1d4 + 1 expended Charges per long rest.
Once per long rest this bell may cast the Catnap spell on 1d4 willing creatures.
Created Saraneth but haven't playtested it yet. The main spell is Mindwrack Binding taken from Conflux-art's Death Denied book.
Saraneth, the Binder - The deep-pitched gong of this bell shackles the dead to the wielder's will. Upon a closer inspection, a faint scent of hot-metal can be detected.
Wonderous item, Legendary (attunement optional)
This bell has Charges equal to half your character level (minimum 2). While holding it, you can use an action to ring the bell and expend 5 charges to send a pulse of terrible mental static that briefly overwhelms the faculties of nearby creatures. Each creature within 15 feet of you must succeed on a Wisdom saving throw or be Paralyzed until the end of your next turn. You may expend an additional charges to increase the radius by 15 feet for each charge.
Additional Spells. While holding it, you can use an action to ring the bell and expend 1 or more of its Charges to cast the following spells from it: Dominate Beast (2 charges), Dominate Person (3 charges), Dominate Monster (6 charges) on all creatures that can hear it within 15 feet. You can increase the spell slot level by one and range by 15 feet for each additional charge you expend.
Before casting the spell, make a DC 19 Charisma (Performance) check. If attuned, add your proficiency modifier to this check. On a successful check, creatures friendly to you are immune to the effects of the spell while resolving the effects of the spell. On a failed check, resolve the effects of the spell and take 1d4 necrotic damage at the start of each turn you maintain concentration until the spell ends. This damage cannot be reduced in any way.
The bell regains 1d4 + 1 expended Charges per long rest.