I've always liked the idea of magic items that scale as the characters do, and one item in particular has always seemed ideal to me for this:
The Nine Lives Stealer
Now, I really dislike how it plays on the DMG, because it's basically just really useful against low HP enemies (and thus pretty useless).
But I love the name and I love the art. So in my head, it became this crazy sword that devours souls and becomes more and more powerful as it does so.
So:
Nine Live Stealer legendary, (requires attunement)
Whenever you bring a creature to 0 HP using this weapon, you can rip their soul out of their body, killing them instantly and trapping their soul inside one of the the blade's nine gems.
Keep track of which creature's souls you have trapped.
Add up the total proficiency bonuses of all creatures trapped inside the sword: the total is referred to as your Soul Score. Your Soul Score gives you different bonuses, as shown below (all effects are cumulative)
Soul Score (after 46 these are just speculative)
-0-17: You can use a bonus action to change the shape of the weapon, turning it into any simple or martial melee weapon. Its magical properties are the same in each form.
-18-27: +1 to attack and damage rolls
-28-36: +2
-37-45: +3
-46-50: Heart Seeking Splinters (I was thinking about Krell's Black Axe from Warhammer here: the effect would be maybe -1d4 max hit points per hour, useable once per day). Crits on 19-20
-51-55: 3 charges per day to stun an enemy for 1 round (with save?) and add 1d10 psychic dmg
-56-60: Dissonant Whispers, Darkness, Speak With Dead, Sickening Radiance, Enervation, Maddening Darkness, Psychic Scream (All consuming charges = to their level, save DC 18)
-61-65: ?
-66: ?
You can also consume trapped souls as a bonus action to gain temporary bonuses:
-The sword gains a number of charges equal to the proficiency bonus of the creature consumed
-You gain the ability to cast all the spells the creature had prepared when it died without expending spell slots. If you wish, you can cast a spell with a casting time of 1 bonus action as an action. This benefit lasts until the beginning of your next turn. If a spell requires material components, you may eschew them as long as they don't have a cost in GP.
-You gain proficiency in one skill, tool or language the creature was proficient in. You gain proficiency in the chosen skill, tool, or language for 1 hour. If you are already proficient with the skill or tool, you double your proficiency bonus with it. If the creature's proficiency bonus is higher than yours, you ma use is instead of yours (doubling it as normal if you are already proficient in the chosen skill).
-You gain temporary hit points = 5 x the creature's proficiency bonus.
-You gain one of the creature's special traits for one round.
-You add the creature's proficiency bonus to all attack or damage rolls you make until the beginning of your next turn.
Whenever you consume the soul of a creature with a proficiency bonus of +3 or +2 in this manner, all souls with the same proficiency bonus or lower are also consumed with no additional benefit.
I have some commentary on these features and a little backstory on the weapon, but I'll just edit in tomorrow since it's late.
Also, it's reaaally really powerful, so I need to give it a good curse to go along with it.
Would love to hear your guys' advice
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