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 two cursed longswords, a Polymorph Blade, and a Blade of the Medusa, which they both decursed with a Remove Curse spell.
The Polymorph Longsword states 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.
The Longsword of the Medusa restrains and petrifies the target.
When you attack a creature with this magic weapon and roll a 20 on the attack roll, the creature must make a DC 15 Constitution saving throw in addition to suffering the attack’s normal effects. On a failed save, the creature is restrained and must make another Constitution saving throw at the end of each of its turns. If it successfully saves against this effect three times, the effect ends. If it fails its saves three times, it is turned to stone and subjected to the petrified condition for 1 hour.
They have now decided to sell both of them (we follow a homebrew world where some places have magical item markets), and I was wondering what would be an adequate value for both weapons. They are both very rare weapons, and while the Blade of the Medusa does look like a very powerful weapon, the Polymorph Blade does not.
I would value the Medusa Longsword around 15000g (a bit below a +3 Longsword), and 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 worth it) and can backfire (suddenly facing 136HP of TRex instead of a random minion). However, Restraining the target is always useful. Both effects only occur on a natural-20, so it should be rare. I like to have some input from the community on my value estimation.