Just started a new campaign. Players are very enthusiastic. I'm enjoying myself. If there is a greater rush than GMming, I don't know of it.
One of the players made an excellent rules suggestion which I adopted on the spot, but I thought I'd run past your redoubtable knowledge, experience and grognardery to see if it's been considered before, and if there are any known repercussions.
Let me paint you a vignette. The background of it is that the magician in question has a sword as his Talisman. He's just opened it, and is looking forward to filling it with powerful defensive magics. However, before he can do so, he gets ambushed by an ogre during a vis hunt. (Play had ground down a little, and I wanted to give the party a fight to get their blood pounding again.)
"I stab the ogre with my magic sword!" the player exclaims.
"His magic resistance defends against it", I reply.
He's disappointed. He wanted a magical sword, and his magical sword is now worse than a mundane one. "So I should just use a regular sword against things with magic resistance?" the player queries.
"Many ogre-slayers carry mundane swords for just this reason."
The player mulls for a moment; this is different from the worldview which D&D has taught him. Then, a light gleams in his eyes: "Why don't I just enchant some penetration into the sword, then?"
"..."
"The wand of Crystal Dart which the other character is using, has enough penetration to get through its magic resistance; that's the point of the wand. If you put the same spell into the sword, then the spell would be able to penetrate, so surely the sword itself would also be able to penetrate?"
I'm not sure what to respond. I mull it over. On the one hand, he's right; it's absurd to say that the ogre's magic resistance blocks a weapon which is enchanted in such a way as to specifically be able to pierce this magic resistance. On the other hand, if I say yes, what am I agreeing to?
If in doubt, say yes. It teaches your players to be creative. I can always backpeddle later.
"Yes", I say, "I think that's an excellent idea. Why don't you use that as your inaugural lab project?"
The player rubs his hands with glee and dives into the enchantment rules as soon as the fight is done. Half an hour later or so, he looks up at me again with the rapacious eyes of a munchkin who has come up with something he's proud of.
"Do I have to put a magical effect into it?"
"I'm sorry? I thought you were enchanting an item?"
"I am. But all I want is the penetration, which costs a level for 2 points. I don't actually need the effect itself. The more powerful the magic I put into it, the less penetrating I can make the sword's mundane usage. Logically, the best thing for me to do is therefore either to find some banal effect with extremely low level; or simply have no effect at all."
Hmmmm. He's got a point. "That sounds reasonable. Do it." I reach for the doritos and munch a few as the players fall into in-character bickering.
The only problem that I can see, would come from if he now enchants the sword with damage-enhancing effects. (For example, Edge of the Razor). My own knee-jerk ruling on this would be that Edge of the Razor would then need to have its own penetration total built in, as would any other damage-enhancing or negative-status-effect-granting effects.
Thoughts?