AFAIK, yes they could (as a use-activated one-shot item, for example). You might consider a couple of the commonly posted houserules rather than an outright ban. Off the top of my head:
- Change the DC to +5 + spell level
- Make it so caster level can't be bypassed by a DC increase
- Remove the DC increase altogether (though they could still do it with UMB and a scroll)
I'm sure there were (and will be) other suggestions. Those are just the ones I remember.
Pathfinder Adventure Path Charter Subscriber; Pathfinder Modules, Roleplaying Game Subscriber
+1 to VRMH
Any magic item not outlined in the books is up to GM approval. Don't ban the feat, just make sure you talk to players about such feats if they intend to take them, and ask what they plan to do with it. If they intend something you know you'll not approve of, let them know ahead of time, and thus save the angst of taking a feat that they can't use for their intended purpose.
Lets him create greater demiplane? With the master craftsman feat? One of my players is claiming this, about to ban the feat from play.
At a quick glance, I couldn't find any non-Artifact magic item that allow you to do this. So, that means you are entering the realm of custom magic items, which are encouraged to be vetted before getting approval.
Assuming you were to allow the kind of madness this would require, your player is looking at creating an item that casts a 9th Level Spell (Create Demiplane, Greater) AND also casts Permanency to make it last. The rules for making such an item are there and following the table turns out an item costing a not-so-high amount of money (approx. 100k gp at my VERY rough guess).
Now the custom item table is to be considered mainly a guideline and shouldn't be considered gospel.
All that said, I'm not sure there is anything particularly unbalancing about allowing the players to have a demiplane. It might even be kind of cool.
Master Craftsman is mainly a feat that allows not-caster characters to build their own magic items (+1 swords and such things) and tries to encourage the trope of a master smith who is so talented that they can make magic without having it themselves.
If this isn't good with your game, then the group should agree that such shenanigans aren't ok. If it is cool, then run with it and have fun.
Actually, as a one-use item that just cast the spell once and then cast permanency, it comes out to 33,535 gp. Compare that to the cost of getting a caster to cast it for them (assuming such a caster could be found) which is 24,705 gp.
A different version of the item would be a use-activated greater create demiplane which works out to 306,000 gp. Then they could make it as big as they like, but they'd have to recast it every couple of weeks.
An item with both use-activated greater demiplane and permanency would cost 463,500. For that, they'd have all the land and buildings they wanted, and portals to anywhere they knew very well. You should compare that to them buying a castle and a gate item.
Throw the ability to WISH 5/day in on top of it for a simple +5 DC chance and few more gold! Woot!
(stupidest skill mod in the game IMHO... IMHO it should be 5 + Spell level (if not caster level) added per spell "not used" in the creation)
You've lost your mind sir. Wish 5/day would cost 1,250,000 gp in gold piece just to cover the material components price; before factoring in the 114,750 gp price tag of it being a 9th level spell-trigger; or the 275,400 gp if it was usable by anyone; and that's before factoring in the other capabilities of the item.
EDIT: To put that into perspective, you would need about one and a half times a 20th level character's entire wealth by level. So even if you were to craft it yourself, you'd first need to find a nice quiet plane with some slowed or time-stopped traits to begin your work on; and convert essentially your entire WBL into having wish 5/day.
Given that wish has been extremely nerfed from 3.x to Pathfinder; having wish 5/day is surprisingly mild. It is, in essence, saying that the caster can cast most any spell of 6th level or lower with no restrictions, or 8th or lower with restrictions, five times per day. The +5 inherent modifiers can be gotten way cheaper much earlier and with less effort; and nothing else wish does is really that impressive.
A fighter can lose a lot of his power, focusing on crafting. I see no balance issue with letting him have the feat.
Balance issues comes into play with custom magic items. No right minded DM would allow a use activated quickened true strike item, and yet there are rules for it. Remember, the custom magic item rules are guidelines. As the DM, you are the final arbiter of price, and availability.