D&D 5E I'm sure this has been done before....gates/teleports/lots of magic....attracting unwelcome attention...

[Casimir Liber]

I was trying to institute this in my homebrew as an explanation for why people aren't more free and easy with magic: namely, that using alot of magic, particularly teleports, gates and summoning critters, weakens the fabric of the material plane and risks attracting unwelcome extraplanar visitors. Has anyone developed any firm rules/probabilities in a homebrew or otherwise seen something published in a campagin/module/dungeon?

 

[R_J_K75]

I seem to remember in 2E FR that gates can become unstable and unpredictable the older they are. Halaster uses gates to other planes and primes to bring monsters into Undermountain. Ive dont recall any firm rules other than the stipulations of how the gate works were determined when they are created, permanent ones at least. Im not positive but I think the 2E book Wizards and Rogues of the Realms had a page or two on gates, one of the FR books from around 95-97 had it somewhere. The teleport spell had a mishap table too, but 5E seems a little more forgiving than I remember of earlier editions. My advice is, if its something you want in your campaign just make up whatever. Magic is unpredictable at best so I wouldnt bother quantifying it any further than when it suits the game have some mishap happen or random monster appear. At the most a short 1d100 table should suit your needs as long as you let spell caster players know that casting certain spells can lead to odd results.

 

[Lyxen]

I did this in my major campaign, where the world had actually been broken into shards during the previous war of the gods, and pieces where hanging on by threads which also served as wormholes between the pieces. So there were lots of portals around, but it was also extremely unstable, with pieces of the far realm poking in at any disturbance. Once you get attacked by nasties like chuuls, carrion crawlers, grells, grisck, nothics when you don't expect it or in the middle of fights, you start to be weary. Of course, at the start, there were no hints about what provoked the breaches, the PCs had to piece it together themselves, and it took a while because the prevalence of portals seemed to indicate that there was nothing wrong in creating more...

 

[Quartz]

In the (Fantasy) Hero System there is a Limitation called 'Noisy' which means that anyone within range knows a spell was cast. Or you could create a Limitation: Summons nasty beastie 8- or Summons Very Nasty Beastie 5-

The take-away though is that it's important to let players know beforehand. Don't spring it on them.

 

[Casimir Liber]

In the (Fantasy) Hero System there is a Limitation called 'Noisy' which means that anyone within range knows a spell was cast. Or you could create a Limitation: Summons nasty beastie 8- or Summons Very Nasty Beastie 5-

The take-away though is that it's important to let players know beforehand. Don't spring it on them.

Yeah absolutely - the main way I'd do that is many experienced/canny NPCs voicing in mummerset accent, "now ya wanna be careful with magic like, don' wanna attract too much attention from them what you'd rather remain hidden...." (cue dramatic music)

 

[LordEntrails]

Firm rules, nope. Most rules would use random chances or tables anyway, so just make things happen by DM fiat. Roll if you want the players to think it's random. To keep it fro. Becoming predictable, use a 1d6 or such to determine the next time something happens.

 

[CubicsRube]

Not firm rules no. But in my D&D campaigns I rule that casting spells shortens the length of the casters lifespan, cantrips a day, 1-2 levels a week, 3-5 a month, and 6+ a year. Kind of an inspiration from earlier editions.

It provides an easy explanation why cleeics aren't raising the dead every day and wizards aren't popping off fireballs every day. Maybe a few cantrips a day, cause hey, who's going to notice a day or two less in their life huh? But casting a 9th level spell better be worth it of you're cutting your own life shorter by a year.

As a side effect it gives an explanation that I like as to why Elves in particular are seen as more "magical". They have longer lifespans and will more readily use magic than shorter lived species.

 

[Oofta]

I describe teleportation as simply taking a short trip, you are awake and aware of your surroundings as a blur of movement. You are, in effect taking a shortcut through another dimension, being pulled along by the power of the spell.

Having said that I don't have a problem with short distance teleport, it's not that game breaking. Even teleportation circle isn't that bad, the sequences for the targets are closely kept secrets and often just lead to a sealed room with various glyphs and other protections.

The problem child is the teleport spell and monsters that can just teleport wherever they like. There is the forbiddance spell, and it would make sense that important places of power would have them done simply as part of the construction cost. It takes 30 days, but 1,000 GP cost is nothing compared to someone just teleporting into inner keep to start an invasion.

Beyond that? My campaign world has magic that isn't in the book. One of those is the ability to redirect teleportation, which can be worse. Current campaign though? I just ban the teleport spell because people have decided that it's too dangerous. Too many areas have been corrupted and you may end up "stuck" in the alternate dimension. If I really want people to teleport hither and yon for story reasons, then getting access to teleportation circles is part of the campaign.

 

[Steampunkette]

So let's see... I'd probably break this down into two separate sections:

Regional Instability: Places where powerful magics have been used many times grow strange. This can manifest in things like Hauntings, where the veil between life and death is thin, but also locales that are demon-haunted, specifically. While demons do not physically prowl in such a location, they can affect the world with horror and pain through the thinning veil, and will do whatever they can to make it thinner. Once it reaches a certain point, they can possess people foolish enough to spend significant time in such a place.

Regional Instability is a value on a d20 that a DM assigns to an area before the adventure starts. Each day that creatures are within the area, the DM rolls to check whether or not something on the other side notices them. In a demon-haunted locale such notice is immediately malicious and can manifest in hallucinations, physical harm (Useless expenditure of Hit Dice), and more. While undead and other things tend to haunt toward a less violent purpose. With a high enough roll, or enough further thinning of the veil through magic, the entities on the other side -can- punch through.

Further, whenever certain kinds of magic are used in the unstable area, make a d20 roll against the rating. If you roll below the Regional Instability, your spell allows things from the other side to burst loose.

Someone entering an area of Regional Instability who has a higher Personal Stability rating than the region -automatically- attracts attention from whatever is near the thinning veil.

Personal Instability: Powerful characters, by their very nature, attract attention through the veil. Each character has a Personal Instability rating based on their level and abilities, as well as their actions.

Full Spellcasters have an Instability Rating equal to their Level.
Half-Casters, such as Eldritch Knights and Arcane Tricksters, have an Instability rating equal to 3/4 of their level.
All other characters have an Instability rating equal to 1/2 their hit dice.

This baseline is then modified by character actions.

Notable success +1. If you've saved a Nobleman, for example, or defeated a powerful creature.
Ritual Caster +1: If you've taken part in Ritual Magic within the last month.
Crossed the Veil +2: If you're a Planetouched character, or you've been resurrected from death.

I feel like that makes a solid basis for such a system?

 

[THEMNGMNT]

Well, if you have a magical transporter that bypasses all the walls and guards in your castle, who's to say your enemies couldn't use it, too?