Is this homebrew Bloodstones of Power magic item balanced?

Question

Bloodstones of Power (Small pouch containing 5 stones)
25000 gp

Very rare Magic item

When a PC takes damage of 7.5 per level or higher due to slashing, or piercing damage the character can use the blood from the wound to activate a stone as a bonus action on their opponent's turn. During activation the stone flashed brightly with magical power and then dissolves into nothingness. The stone's magic can cast any 4th level or lower spell on any target within 50 feet in sight of the character with no spell components needed. The spell acts as normal after activation. Concentration is not needed for this magical item. If the character would drop below 0 life points on the attack that damaged them, after activation, they are brought to 1 hp, are prone, stabilized, and have used one successful death saving throw and one failing death saving throw.

Character does not need to be a magic user to use these items.

Answer 1

This needs a great deal of editing

Let's talk about the activation requirement. I think it's a bit unclear. When you say "a PC takes damage of 7.5 per level", do you mean the character's level or the level of the spell they're trying to cast? I assume you mean character level, and that you need to have taken that much damage in a single hit that deals slashing or piercing damage. The rest of my comments in this section will be based on this assumption.

First off, that's going to rapidly become impossible to meet. At 5th level you'd need to take 38 damage in a single blow, which is virtually impossible on a normal hit, and unlikely even on a crit. Even an ancient red dragon maxes out at 22 damage in a single claw attack, or 34 with a crit. By tenth level it's simply impossible to activate this item in most cases, if I've read the rule correctly. (And in case you were thinking of having piercing/slashing damage add up over time until they reach the limit, I don't recommend that -- adding more bookkeeping for just a single item really sucks.)

Second, even if there were monsters that could deal out damage like this, you're going to quickly outpace PC hit point totals for most characters. To even have 7.5 HP per level, a PC needs to have a d10 hit die with a +2 or better Constitution bonus, a d8 hit die with a +3 Con bonus, or a d6 hit die with a whopping +4 Con bonus. This item is functionally limited to the tanky classes like Fighter, Paladin, and Barbarian.

Rules interactions

You say you can "activate a stone as a bonus action on their opponent's turn". Bonus actions happen only during your turn. ("Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.") This item as written is impossible to activate. If you want something to happen during another creature's turn, you have to use a reaction, and you only get one each round. The reaction will need text to explain how it activates when you technically should be dying, or else remove that part of it.

The spell can be cast "on any target within 50 feet in sight of the character". Instead, I recommend just having it cast the spell you choose. Spells already specify their range and targeting requirements (such as being able to see the target), so adding those to the item itself just complicates things unnecessarily.

This is probably a bad idea because players are people

But even if the rest of this is resolved, the big problem is how this will play at the table. You're imagining that the player gets one chance to cast a spell and then the game resumes. But is that really what's going to happen? Is the player going to already know exactly what they want? Or is this going to turn into "okay hold on, I need to look at the entire list of spells for twenty minutes to pick out the one I want to cast"? There's a reason spell scrolls and glyphs of warding have to be specified ahead of time. Don't introduce an item that's likely to stop your game cold.

Answer 2

Looks OK if risky, and has technical issues

First, this allows you to cast a triggered spell like glyph of warding but move them around. Second it allows any class to cast any spell under level 5 from any list. This both sounds pretty exploitable, there are few items that allow something like that.

The damage threshold however seems high enough that you would not typically trigger this on purpose on yourself. Even a class with d12 for hit points and +1 Constitution bonus would need to lose nearly their total hp in one go to trigger it, that is a pretty steep price.

However, several mechanics do not work as it is currently worded:

• You cannot take bonus actions outside your turn. This would need to say you can use a reaction.

• Normally reactions only happen after the trigger finishes. By then you may be dying and unable to use them. I think you would need to word this so that you can use it before you took the damage, which might make this unbalanced (eg Misty Step away to avoid it) or you need language that you need to determine the spell and parameters of the spell in advance.

• You either are dying and unconscious and may have racked up death saves, or you are stable and at 0 hp, or you have 1 hp and are fully operational. You cannot be a mix of those.

• The language for targeting is not using the templating of other spells or effects. It probably should say “any target within 50 feet that you can see and that the spell can target” Otherwise this could cast spells on normally illegal targets wich could cause all kinds of issues.

Lastly, items in 5e unfortunately do not have a fixed gp value.

You may want look at the contingency spell, if you are looking for examples of limitations of spells to store.

Flavor-wise, this seems to be a cool item that allows for some retributive strike or restorative healing when a character (or villain) would be downed by a massive attack.

Answer 3

The edits you've made so far definitely address some issues the item had but I don't think you're out of the woods yet.

When a PC takes damage that would cause them to have 0 HP due to slashing, or piercing damage the character can use the blood from the wound to activate a stone as a reaction on their opponent's turn.

I have two issues with this text:

a) I'd change the wording to refer to the total damage needing to have some component of slashing or piercing to it, regardless of the total makeup. As it stands I could imagine the arguments caused by trying to define whether it was the slashing or the poison damage that dropped the player to 0 hp.

b) "as a reaction on their opponent's turn" - this is too restrictive. There are many situations where the PC is using their reaction in response to a reaction by another creature on the PC's turn. Opportunity attacks are a great example. I try to move and get smacked by an OA that would drop me, yes sir I would like to be able to use the bloodstone at that point.

Lastly, the spell section is weird. What spells am I limited to? Can I specify Power Word Kill? This needs some better rules around it as it is very, very open ended as it is. EDIT: The level of the available spell has been changed to a more reasonable limit, at one point in this post's evolution it wasn't specified at all.