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-   -   Building permanent magical traps with GURPS Magic (http://forums.sjgames.com/showthread.php?t=134671)

Grouchy Chris 04-27-2015 05:05 PM

Building permanent magical traps with GURPS Magic
 
Are there any by-the-book rules on constructing permanent magical traps using the standard magic system given in GURPS Magic?

As I read the rules, a mage can cast, for instance, Link and Fire Cloud to burn anyone who enters a certain area. But this has a few shortcomings: the trap can only fire as many times as the mage casts Fire Cloud, three link spells count as one spell "on" for the mage, limiting further casting, and also it's not entirely clear whether the Link would persist after the caster's death.

The rules on enchantment say (Magic p. 18) that some spells can be used to enchant an area, but Link is not one of them.

So are there any rules using the standard magic system for creating magical traps that last indefinitely and can fire an unlimited number of times, without burdening the caster with a "spell on" penalty? I've looked through the books I've got, but perhaps there's a Pyramid article or something I don't know about.

I'm perfectly comfortable adapting the existing rules to cover this case, but first I'd like to know if someone's already done it.

And yes, I know about Evil Runes from DF2, which create magic effects by fiat. That's not what I'm looking for.

Anthony 04-27-2015 05:09 PM

Re: Building permanent magical traps with GURPS Magic
 
Quote:

Originally Posted by Grouchy Chris (Post 1895135)
The rules on enchantment say (Magic p. 18) that some spells can be used to enchant an area, but Link is not one of them.

"Item: this spell may be cast permanently on any enchanted item". It seems to me that an enchanted area is still an item for these purposes.

Grouchy Chris 04-27-2015 05:19 PM

Re: Building permanent magical traps with GURPS Magic
 
Quote:

Originally Posted by Anthony (Post 1895137)
"Item: this spell may be cast permanently on any enchanted item". It seems to me that an enchanted area is still an item for these purposes.

"Item: this spell may be cast permanently on any enchanted item, to determine the circumstances under which it works." So, yes, you could enchant an area using Avoid, and then cast Link to determine the circumstances under which Avoid works. But that does not get me to a permanent Fire Cloud trap, so that's not what I'm looking for.

Anaraxes 04-27-2015 05:27 PM

Re: Building permanent magical traps with GURPS Magic
 
Just create a self-powered item that can cast Fire Cloud, and add Link to trigger it. "Item" here could be the room, or a particular stone in the wall / ceiling / floor if you prefer.

Anthony 04-27-2015 05:36 PM

Re: Building permanent magical traps with GURPS Magic
 
Quote:

Originally Posted by Grouchy Chris (Post 1895141)
But that does not get me to a permanent Fire Cloud trap, so that's not what I'm looking for.

That's because Fire Cloud does not have a permanent version. You can create a permanent Glue trap with link. Any 'always on' effect will also work, so an item with Fire Cloud and Power 1 can probably be made into a Link effect (there isn't a way of doing this with powerstones, which is a drawback, but not critical).

Grouchy Chris 04-27-2015 05:42 PM

Re: Building permanent magical traps with GURPS Magic
 
Quote:

Originally Posted by Anaraxes (Post 1895144)
Just create a self-powered item that can cast Fire Cloud, and add Link to trigger it. "Item" here could be the room, or a particular stone in the wall / ceiling / floor if you prefer.

No good, because a magic item requires a user. If I create a ring of Fire Cloud and put a Link on it that says it works if someone enters a certain area, then I get a ring that will allow a user to cast Fire Cloud if someone enters a certain area. Hiding the ring under the floorboards does not provide the necessary act of will by a user that activates the magic item.

It's a very minor matter to change the rules and say, "yeah, well, now you can use Link to activate a magic item like that," but as I said, I'd like to know it can be done by-the-book before I go making my own rules.

Anthony 04-27-2015 06:04 PM

Re: Building permanent magical traps with GURPS Magic
 
Quote:

Originally Posted by Grouchy Chris (Post 1895148)
No good, because a magic item requires a user.

An item with a Power enchantment sufficient to cover its casting cost may be classed as 'always on' (see M57), in which case it would qualify for the Link.

Grouchy Chris 04-27-2015 06:41 PM

Re: Building permanent magical traps with GURPS Magic
 
Quote:

Originally Posted by Anthony (Post 1895146)
That's because Fire Cloud does not have a permanent version..

Then this trick is not what I'm looking for. I don't want to be limited to the handful of spells that can be cast as an enchanted area. I want the full gamut of spells, including ones that deal direct damage.

Quote:

Originally Posted by Anthony (Post 1895153)
An item with a Power enchantment sufficient to cover its casting cost may be classed as 'always on' (see M57), in which case it would qualify for the Link.

But the item still requires a user. Magic, p. 19: "Certain magic items are 'always on.' For the item to work, the user must wear or carry it in the usual manner."

Anthony 04-27-2015 06:51 PM

Re: Building permanent magical traps with GURPS Magic
 
Well, if all else fails, use Golem to create a Trap Golem, and have it use the item. Golem is a highly exploitable spell, but this seems a legitimate enough use. Golems cannot spend fatigue, but I don't see any other obstacles to them using magic items.

hal 04-27-2015 08:21 PM

Re: Building permanent magical traps with GURPS Magic
 
One "Permanent" magic trap I employed against a player character was a set of doors that were relatively huge. On the doors, were Huge Bronze Door Knobs that required what looked like two hands to turn them.

They were Hexed.

The poor Thief could not let go of the hexed item once he put both hands on the knob.


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