What would be the gold value of a Polymorph Blade?

Question

We usually follow this homebrew guide for magical item prices, and my players have recently played through the Lost Laboratory of Kwalish adventure. In it, they obtained a cursed longsword, a Polymorph Blade. It casts a Polymorph on the target, randomly ranging from a TRex to a rabbit.

When you attack a creature with this magic weapon and roll a 20 on the attack roll, the creature must make a DC 15 Wisdom saving throw in addition to suffering the attack's normal effects. On a failed save, the creature also suffers the effects of a polymorph spell. Roll a d20 and consult the following table to determine the form the target creature is transformed into.

The blade is cursed.

This weapon is cursed, and becoming attuned to it extends the curse to you. Until the curse is broken with a remove curse spell or similar magic, you are unwilling to part with the weapon. Whenever you attack a creature with this weapon and roll a 1 on the attack roll, you suffer the effect of a polymorph spell for 1 hour, rolling on the table to determine your new form.

They have now decided to sell it (we follow a homebrew world where some places have magical item markets), and I was wondering what would be an adequate value for it. It is very rare, cursed (my players don't really care about that), and does not look too powerful.

I would value the Polymorph Blade around 5000g (a bit over a +2 longsword). My reasoning is that Polymorphing the enemy you're attacking is situational (either there are other enemies to attack or it is not worth it) and can backfire (suddenly facing 136HP of TRex instead of a random minion). On the other hand, it can take the BBEG out of the fight while its minions are overrun, and can also burn legendary resistances. The effect only occurs on a natural-20, so it should be rare. I'd like to have some input from the community on my value estimation.

Answer 1

Cursed items aren't priced in that homebrew pricing

Which makes determining what other cursed items may cost impossible. Unfortunately, I don't think we can provide an equivalent or equivalents to extrapolate cost on this without having a basis for the determination of that.

Anything else would just be an opinion :(

Answer 2

Unfortunately, in combat the Polymorph Blade is probably worse than a standard longsword. You've written that you think it might be valuable because it could turn the BBEG into a rabbit -- but the Polymorph Blade says:

A creature is immune to this effect if it is immune to damage of the weapon's type, is a shapechanger, or has legendary actions.

and the BBEG probably has legendary actions.

On a natural 20, this blade has a chance to use its effect on your opponent -- but on a natural 1 it is guaranteed to use its effect on you. So this effect is actually more likely to happen to you than to your opponent.

As RevenantBacon points out, polymorph is intended as a buff spell; it grants the target an additional pool of hit points. Checking the polymorph table, I see a CR8 T-Rex, a CR7 Giant Ape, a CR4 Elephant, and the remaining forms are CR3 or worse. Your group has finished Lost Laboratory of Kwalish, so they're probably around level ten; if they turn the target into anything smaller than an elephant, they can probably just ignore it until the end of combat and then gang up on it five-to-one. So, even though polymorph does grant a pool of hit points, I think we should regard it as an 85% chance of a severe debuff.

There are exploits. If you really wanted to be polymorphed, you could wear a blindfold (getting disadvantage) and swing wildly at the heavily-armored paladin. Eventually you'd roll a one and get a free polymorph. Some of the creatures on that table have fly speeds or swim speeds; if a character really, really needed to be a giant eagle or hawk for an hour, this weapon could be a big help.

But I don't think we should regard this as a weapon that is usable in combat.

If it were me, I'd probably narrate that the polymorph blade is bought by a spellcaster who wants to use it in experiments. Maybe a wizard thinks she can extract the polymorph effect from the sword and use it to build a magic item that could actually be useful. Maybe a cleric has access to remove curse and wants to try out the polymorph effect recreationally. I'd probably narrate that they pay the group 1000gp for it.

Answer 3

As-is, it's a very low value item, probably less valuable than a mere +1 sword

It would be difficult to find an actual buyer, since anyone who owns a magic shop is going to be smart enough to not buy a cursed item.

That being said, here's my opinion on this items value. As a magic sword, it generally has one purpose: making it easier to kill your target. The polymorph effect from this weapon will literally never further this goal, due to it being random on what the target could turn in to, and them getting free HP for the duration on the change. The value of an item is directly determined by its usefulness to anyone who would/could use it, and a sword that gives your enemy free HP on a crit (likely negating the entire crit) is 100% downside. Anything they turn into that has more HP than what you did on your crit is likely a combat upgrade, and anything with less HP basically just serves to reduce your crit damage.

Alternatively, if they can find the right buyer. Say a wizard who's looking to do some experimentation with that particular enchantment, or perhaps an artificer who wants to basically use it for raw materials in a different magic item he's creating. Both of them might be willing to give out a nice chunk of change for that sword, since the enchantment on it is clearly quite powerful, if rather useless. If this is the case, it could be worth a considerable sum more, possibly as much as 6,000 GP, depending on what they buyer is trying to do with it.