The Repair spell from GURPS Magic is both simultaneously a blessing and a curse in my games.
On the "blessing" side, it's very useful to have players able to quickly and completely repair battle damage or re-assemble broken items. It's not a genre-breaking usage, either, in a word where magical healing spells can repair otherwise permanent damage.
On the curse side, it's very powerful. You can repair just about anything, and it means nothing broken is ever really broken.
My players suggested a really ludicrous use of Repair recently - find delicate treasure, bust them up for easy transport, bag them, and then Repair them (at no penalty, thank to no missing parts). While this is really funny, it's one of those things that violates the spirit of DF to some degree. It was an amusing request and it really got my brain churning about ways to modify Repair to fit the "how are you going to get that delicate stuff home?" quandary. At the same time, you don't want to wield the nerf bat too strongly, or it's a wasted spell.
Here are two solutions:
1) Repair is Temporary
Like spells which create, spells which repair are also temporary. The Repair spell duration changes from "Permanent" to "24 hours." At the end of that time, the item reverts to its pre-repair broken state. The secret to permanent Repair (which incidentally costs 10x as much) is a closely-held secret of the mage's guilds and NPC enchanters.
Note: It's a very simple change to implement but a very strong change. It makes the spell much less useful. Another way around it would be to say it's something like 2x, 5x, or 10x cost to do it permanently but anyone can do it.
2) Repair Takes Skill
To repair, you need:
- an appropriate craft skill at 12+ to repair the item. Armoury (Body Armor) for armor, (Weapons) for weapons, Mechanic for machines, Carpentry for etc. If you lack the appropriate skill entirely, you roll at a -4 on Repair. If you have the skill but not at 12+, you roll at a -2.
- to repair an item with missing parts, you need the appropriate craft skill at 15+.
As a bonus, however, if you have an appropriate craft skill at 15+ you can re-roll a critical failure, exactly as if you had Magical Stability (DF11, p. 15). If you also have Magical Stability, you can re-roll twice and take the better result!
Notes: The basically makes the spell a faster, tool-less way to fix things. It also means you really need some expertise to make it fly. On the plus side, solid expertise means you won't mess up, roll an 18, and have the GM say, "Oops, you didn't repair Serena's magical armor, you disintegrated it!"
Still another way to implement that skill 15+ benefit is to just say if you have an appropriate craft skill at all, you can roll against that to turn a critical failure into a normal failure.
3) The Amount of Damage Matters
A trivial repair, where the item is damaged but still fully functional (such as 1-3 penetrations of armor,a crack in a vase, or a hole in a canteen): +3 to skill
Typical repair, where the item is broken and non-functional (such as a typical weapon breakage): +0
Badly damage items (-HP and below): -2 per -1xHP.
A completely destroyed item (-5xHP) gives a -10. Missing parts gives a -5 (common if destroyed with corrosion, burning, or explosive damage, or if destroyed piecemeal or over a large area). Combined, a totally destroyed item with missing parts is a -15 to the spell.
Notes: This takes the most work, although a GM can pretty easily assign a penalty from -0 to -10. This also assumes most "your weapon breaks" results takes your weapon to 0 HP and a failed HT roll, per B483. This gives a range of +3 to -15 to Repair items. Obviously, if you take the delicate glasswear and break it up and put it in a sack, or slice up the tapestry into ribbons for easy carrying by your various henchmen, you're probably rolling at -10 even if you ensure you have 100% of the parts!
This also leverages the HP/Damage to Objects rules from 4e nicely, in my opinion.
Other rulings I've made with repair:
Repair fixes the medium, not the message. In other words, a book that's turned to dust can be repaired into a blank book. You can't repair erased pencil marks, chalk marks, etc.
When in doubt, parts are missing. That -5 for missing parts is critical to keeping Repair as a useful spell but not a way to grind things to portable bits and then re-assemble them, or claim that grenades are re-usable items with a mere Repair roll.
Raw materials must match exactly. "Teak" is "teak," not "some wood." Any gold is fine for gold filigree, like in the example in the spell, but missing bits of your very fine sword must be high-quality steel, broken orichalcum mail links need orichalcum to fix, and broken glass needs glass, not sand. The materials must only need working, not changing. No raw materials? The spell fails.
You must know what it is. Or at least have a pretty good idea. If you don't, it's -5 on the spell. No "I Repair that pile of dust and see what it was!" Find out first to avoid that -5.
What about Felltower?
I'm probably going with option 3, although I really like the "Craft skill at 15+ acts as a stabilizer" from #2, and I think that's a good way to go. I may even allow Complementary use - a warrior with Armoury (Body Armor)-15 can make a flat skill roll (with any penalties for the amount damaged) to see if he can act as a stabilizer to re-roll critical failures.
So yes, the "sack full of broken chairs and crystal goblets and paintings" will work for them, given good enough rolls . . . after all most of those rolls will be at -10 or so.