Mephit
Mephits are a species of imp-like elemental monsters native to the Elemental Planes of Dungeons & Dragons. Coming in a vast array of subspecies based on particular elements, their appearances, abilities and personalities all differ depending on their precise elemental affinity. The one trait they share in common is that they are all incredibly annoying.
Mephits proliferated with the Planescape setting, which expanded their numbers hugely. Come 5th edition, however, and they suffered a huge setback; to fit the new variant of the Great Wheel, they were stripped of most of their member species and reduced to only six races; Dust Mephits, Ice Mephits, Magma Mephits, Mud Mephits, Smoke Mephits, and Steam Mephits. This new lore is that mephits are only born when two (or possibly more) types of elemental energy interweave, which is also why they tend to be weaker than pure elementals.
In Planescape lore, there's actually an established form of code language involving sending mephits to people you don't like, where the type(s) of mephit sent and the number of them sent conveys different responses or information. For obvious reasons, you only send mephits to rivals, enemies and other people you just don't like. The precise details of the code?
- Air: The gift of an air mephit indicates that the sender intends to either ambush the recipient or politically betray them. Naturally, these are usually timed to arrive after the plot is already in motion.
- Ash: These mephits are normally only sent to get the last word in, as they indicate a very strong and very rude refusal to correspond with the recipient anymore. They signal the recipient is no longer seen as being worth talking talk.
- Dust: Receiving a Dust Mephit is a subtle threat, typically indicating that the giver has recognized some plot you are holding against him.
- Earth: Indicating a strong refusal to concede to demands, sending an Earth Mephit to somebody is a very firm declaration of "NO!"
- Fire: These mephits indicate displeasure with some recent action of the recipient's, with the number sent indicating just how mad the sender is.
- Ice: These mephits indicate that the recipient is now officially forbidden from entering the home of the sender, with the number of Ice Mephits sent roughly indicating just how harshly they will be punished if they try.
- Lightning: Serving as a simultaneous warning and boast, the gift of a Lightning Mephit cautions the recipient to reconsider their tactics against the sender, as the sender has acquired some hidden ally who can swing things in their favor. These mephits are often, but not always, a bluff.
- Magma: One of these mephits is only sent in response to the sender having recently bested the recipient in some intellectual or diplomatic challenge. Basically, it's the sender's way of gloating.
- Mineral: An exception to the general rule of mephit code, the gift of a Mineral Mephit indicates that the sender is willing to compromise on something and is asking for more direct communication to be opened.
- Mist: Getting one of these indicates that someone close to you is an assassin, but the mephit itself almost never knows who. Given the usual audience for mephit codes, it's typically intended to inspire paranoia.
- Ooze: These mephits are intended as sarcastic gifts, and basically serve as a way for the sender to say that the recipient is a weakling.
- Radiant: Like the Mineral Mephits, these are an exception to the generally hostile nature of the mephit code. The gift of a Radiant Mephit is essentially like receiving a white flag; it indicates that the sender wants to declare a truce.
- Salt: As the most unpleasant of all mephits, sending somebody a Salt Mephit serves as a declaration of open warfare between sender and recipient.
- Smoke: Similar in nature to Salt Mephits, but less extreme; the gift of a Smoke Mephit is a sign of insolence and contempt, and is usually used to declare a vendetta.
- Steam: Serving as opposite of the Earth Mephit, the gift of a Steam Mephit indicates that the sender is agreeing to some request of the recipient. There is, however, a connotation of gloating — it serves as a way to say "yes, but I told you so!"
- Void: As mentioned above, the Plane of Void (or Vacuum, depending on where you look) has no native mephits, so "to get a Void Mephit" means to never get a reply.
- Water: Serving as formal answer to an Air Mephit, the gift of a Water Mephit indicates a sarcastic congratulation on a failed attempt by the recipient to trap or plot against the sender.
The Mimir fansite also adds the Shadow Mephit, which, in the Mephit Code, means that one of the recipient's enemies has discovered one of the recipient's plans and is now subverting that plan by manipulating it to their own ends. For obvious reasons, this is the most terrifying mephit it's possible to send to beings that fancy themselves The Chessmaster, although fear of Gone Horribly Right keeps the vast majority of people "honest" and so refusing to use Shadow Mephits for bluff messages.