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

[Casimir Liber]

Okay - so small chance of random effects leads to some sort of d100 table with the following (will flesh this out anon):

*Attracts some extraplanar monster (list to come)
*creates rift to random extraplanar location (list to come) that sucks in victims within 1d100 feet (DC 15 STR check to resist?)
*causes random weather-like effect (stinking cloud/fog/rain/hot rain/cloudkill/fireball/chain lightning)


can anyone think of any other broad categories?

 

[jgsugden]

I have not used the instability angle, but people are very hesitant when it comes to teleportation magic, and in particular teleportation circles, in my setting. Installing a Teleportation Circle in your city creates a huge liability. If an enemy finds out the combination that triggers the circle, they can launch huge invading forces through it with no warning. You can send hundreds of troops through a circle - or worse.

As a result, many major cities outlaw teleportation circles within a radius of the city in my setting. In some, the circles are allowed, but magic is used to hide their "combination" from prying eyes (although given the was magic can be used, it is usually not too hard to discover the combination). Others place huge obstructions over their circles when they are not in authorized use.

While teleportation and other magics do not have a negative impact on the stability of the regions, my setting is already a bit unstable. In my setting, the Far Realms crashed into the Known Universe tens of thousands of years ago and fractured it, resulting in the creation of the reflective realms - the Shadowfell, Feywild and Ethereal Planes. There are a lot of places where these realms connect back to the Prime Material plane and you can walk between the planes. Further destabilizing would just muddy the waters for storytelling, I think.

 

[J.Quondam]

Okay - so small chance of random effects leads to some sort of d100 table with the following (will flesh this out anon):

*Attracts some extraplanar monster (list to come)
*creates rift to random extraplanar location (list to come) that sucks in victims within 1d100 feet (DC 15 STR check to resist?)
*causes random weather-like effect (stinking cloud/fog/rain/hot rain/cloudkill/fireball/chain lightning)


can anyone think of any other broad categories?

Maybe
*deposits characters and/or items into the ethereal
*destroy/empty/banish extradimensional spaces (including magic items and spell effects)
*open micro-rift onto an elemental plane, causing random elemental effect (eg, flood, firestorm, tornado, etc)
*gravity changes direction (choose randomly) near gate
*gate emanates damaging aura of random energy type

 

[Imaculata]

In my Homebrew setting, the oldest gates are those that are often deemed the most stable. But since anything can come through at any moment, the gates are surrounded by a gatehouse and a dedicated squad of soldiers, ready to fend off any intruders.

New gates can be unstable. They can disappear and reappear, they can move around while leaving a path of destruction as they swallow part of the land. They can cause flooding when there is a body of water on the other side. And the worst kind are so called dead gates: gates with no destination at all. Anything that passes through them is lost in time and space.

 

[Casimir Liber]

critters that might drop by so far.....

Manes (Monster Manual , pg. 60) - abyss

Abyssal chicken (Baldur's Gate: Descent into Avernus , pg. 97) - abyss

Dretch (Basic Rules , pg. 270) - abyss

Plaresh (creature codex, pg 89) - abyss

Wind demon (creature codex, pg 93) - abyss

Cackler (Guildmasters' Guide to Ravnica , pg. 195) - abyss

Imp (Basic Rules , pg. 277) - 9 hells

Fire imp (creature codex, pg 103)- 9 hells

Maw demon (Volo's Guide to Monsters , pg. 137) - abyss

Quasit (Basic Rules , pg. 273) - abyss

Vargouille (Volo's Guide to Monsters , pg. 195) - pandemonium

Geonid (The Tortle Package)- elemental

Mephit - mud/smoke/steam/dust/ice/magma - elemental

Magmin (Basic Rules , pg. 329)- elemental

Fire snake (Monster Manual , pg. 265)- elemental

shadow (Basic Rules , pg. 344)- demiplane of shadow

spectre (Basic Rules , pg. 346) - negative material

star spawn grue (Mordenkainen’s Tome of Foes , pg. 234) - astral

berbalang (Mordenkainen’s Tome of Foes , pg. 120) - astral

gumienniki (creature codex, pg 213) - any lower

hound of tindalos (creature codex, pg 221) - astral

kuunganisha (creature codex, pg 245) - any lower

wind weasel (creature codex, pg 375) - elemental/feywild

arrowhawk (codex of inner planes pg 63) - elemental

cinderbones (codex of inner planes pg 68) -elemental

firefly (codex of inner planes pg 77) - elemental

nyth (codex of inner planes pg 95) - elemental

swarm of stormworms (codex of inner planes pg 104) - elemental

hellcat (tome of horrors pg 198) - lower

fire crab (tome of horrors pg 145) - elemental