Usually a player character goes out to slay a monster and take the magical item it guards. But in my current game I had set that up rather differently for one location and sets of magical items.
The various potent magical items were made by a wizard who had a special little version of the permanency spell. For OSR or D20 equivalence, this version of permanency did not cause a loss of con, xp or what have you from the wizard. Magic item factory right? Kinda.
Magic has a price, and rather than the caster being harmed this had a secondary side effect. Somewhere in the surrounding area (a large area the more powerful the spell being made permanent) a monster would spawn. The power of the monster is likewise related to the power of the enchantment to be made permanent. This monster is always malevolent, seeking to cause destruction and ruin (especially to the caster). But the enchantment will only be held permanent while the creature lives.
So the first question the party comes to is whether or not to slay the giant jellyfish comprised entirely of flame as it destroys a village or keep their +3 sword. The next question is what to do with the spell when the party's wizard gets a hold of it. Giving the player a +4 sword is so easy..how hard can it be to track down and capture a monster anyway? and what are the odds that all the monsters you keep in locked cages will kill their zoo keeper and escape?
Linking back to Zak's Vornheim, you could potentially add a great twist to the Immortal Zoo adventure.
Cthulhu Fhtagn! Cruz Edition.
5 hours ago