Is this magic item that requires you to permanently sacrifice a hit die to use balanced?

Question

I had an idea about a magic instrument which you can play as an action and permanently sacrifice one hit die (reducing maximum hit points) for a big effect.

As of now, my idea is that you can choose a number of people (equal to proficiency bonus or charisma modifier) which are affected as you start to play, and they get advantage/disadvantage of your choosing. You can maintain this effect if you use your action in the following turns. For each turn you play can affect 1 more creature. For each further minute you play the instrument you need to sacrifice 1 hit die more.

If a creature was subjected to this effect in the past you can use your action to cast Bane or Bless without components and concentration.

I'm not sure if that is balanced, too powerful or too weak. The most answers I got elsewhere were like "I don't use thing where I need to permanently sacrifice my HP"

edit:

• Disadvantage/advantage for attacks, save and maybe skill checks.
• you can cast Bane/ bless with this instrument for 1 action and no concentration.(other Casting restrictions are still in effect like range or saves)
• the hit point maximum would decrease (only the rolled HP, not Con Modifier)
• the loss of your Hit Dice is permanent and can't be healed through spells like greater restoration. maybe a Adventure for that.

It doesn´t matter, that others don´t use it. I will use it.

Answer 1

"Too weak" in the sense that the cost is too great. No one would ever use this in traditional campaigns.

Permanent loss of hit dice and permanent reduction in hit points is far too great a cost. If you are playing a one-shot character, then maybe it does not matter, but for a traditional campaign, having a permanent cost of hit dice means each time you use the item, you will pay for it for the rest of the campaign. It's just not worth it.

Compare to the Aberrant Dragonmark optional feature: a hit die is worth a permanent Epic Boon.

The Aberrant Dragonmark feat has an optional feature that involves the permanent loss of a hit die:

At the DM’s option, a character who has the Aberrant Dragonmark feat has a chance of manifesting greater power. Upon reaching 10th level, such a character has a 10 percent chance of gaining an epic boon from among the options in chapter 7 of the Dungeon Master’s Guide. If the character fails to gain a boon, they have a 10 percent chance the next time they gain a level.

If the character gains a boon, the DM chooses it or determines it randomly. The character also permanently loses one of their Hit Dice, and their hit point maximum is reduced by an amount equal to a roll of that die plus their Constitution modifier (minimum reduction of 1). This reduction can’t be reversed by any means.

This feature has the same cost as one use of your magic item, but grants a permanent epic boon, most of which are extremely powerful:

Boon of Magic Resistance. You have advantage on saving throws against spells and other magical effects.

Boon of Irresistible Offense. You can bypass the damage resistances of any creature.

Boon of Skill Proficiency. You gain proficiency in all skills.

Boon of High Magic. You gain one 9th-level spell slot, provided that you already have one.

And there are many more. These are some examples of the value the rules place on the permanent loss of a single hit die.

Answer 2

Players don't like to pay permanent costs for temporary effects.

It doesn't matter if the effect is balanced or not, because players aren't going to use it. Players don't like making permanent sacrifices for temporary gains. They overestimate the value of permanent effects, and underestimate temporary ones. That means that it's nigh impossible to make an effect like this that is both balanced and feels balanced. Either it's too powerful to give to players, or they think it's too weak to use, or both.

Answer 3

Permanent loss of a hit dice is a significant penalty. The only time a typical player is going to use such an item is when they believe the party will be defeated if they don't. It is not guaranteed that this will ever happen during a campaign - even if the party are losing, they may not realise how bad things are until the point where the item will no longer be able to save them (for example, if the item owner is already unconscious).

So the item might never be used. Or it might, say, be used a couple of times, to trivialise boss battles that would otherwise have been challenging, or to survive a battle that is clearly beyond their normal capabilities (probably thrown at them by the GM purely to force them to use the magic item).

If that's not the intention, you might consider making it an item that costs a single permanent hit point, in exchange for somewhat reduced bonuses.

Answer 4

This is, as several people have mentioned, actually way too expensive to use and would be relegated to the bottom drawer of the players arsenal.

Consider a typical campaign. How often are you fighting?

I'll assume a single campaign requires at least 20 fights, some of which will be quite easy. Those characters may level a couple of times from this. Because we gain a hitdie for each level, for a single combat with bonuses from the item, you'll start every subsequent combat with hitpoints as if you were a level lower. This also means that you could potentially go into combat as a level 1 (1 hit die) after having used it a couple of times. This also means that if you want to use it as a general tool, you will eventually die; you'll be unlikely to level up as fast as you're losing hitpoints.

Also the players, who, given a challenge need to complete it together, will get tired of defending the bard every battle because they're so squishy.