So, Bind Soul is thematically a pretty cool spell. You yank away some dying sucker's spirit, stick it in a pretty gem, and your victim gets to spend the afterlife as a necklace.
It seems to me though that all these polished-up black sapphires would make pretty great magical reagents, either for the crafting of items (e.g. variant staffs), or in rituals for the creation of sapient undead.
We don't exactly have item creation rules yet, but I feel like we can maybe make some educated guesses as to approximate level and price, and I'm kind of curious to see what people manage to cook up.
So, with that in mind, me first with a ghost in a bottle.
Item 12, Uncommon
Traits Magical, Necromancy
Price 1900 GP
Bulk L
Activate 3 actions (command, interact); Frequency Once per hour; Effect The bottle casts unseen servant to your specifications. Twice a day when you activate the bottle, you may instead order the bottle to summon a ghost with the statistics of a ghost commoner, as if the bottle had cast a 5th-level summon spell. While the unseen servant or ghost is summoned, you control it for as long as you spend an action each round to Sustain the Activation. If you do not Sustain the Activation, the effect ends, causing the spirit to return to the bottle.
Craft Requirements Supply a black sapphire worth 200 GP or more, containing the soul of a 2nd-level or higher creature.