Spoiler warning!
This article contains plot spoilers. If you do not yet know of this information, it is recommended that you read at your own risk or not at all.
On bulletin boards throughout the game, you might be able to see small graffiti that says "Kill the rats!". These date back to the days of the Rat Plague. The very same graffiti can also be seen in The Tales from Dunwall, and of course throughout Dishonored.
The phrase "Minted Under Imperial Authority" is stamped on all silver and gold ingots in the game. Back in Dishonored, ingots minted during Hiram Burrows rule were stamped with "Minted Under Regency Authority".
The icon of the pistol on the top-left corner of the screen actually shows how many bullets you have left before you have to reload.
A few details about the Grand Guard's uniform and equipment:
The equivalents of Dunwall's Lower City Watch and City Watch guards seem to be merged into a single group in the Grand Guards. It is, however, easy to distinguish the two types as they wear slightly different uniforms. One type of Guards doesn't have helmets, wears backpacks, and looks thinner than guards of the other type.
Elite and Veteran Guards also wear slightly different uniforms. Elites wear silver helmets, while Veterans wear Golden ones with red plumes.
Some Veterans shoot Explosive Bullets, and you can use Time Stop to grab them even before you acquire the blueprint.
Some regular Grand Guards wear black armoured vest that protect them from ranged attacks (most projectiles ricochet off the vests and Electrical Bursts in Death of the Outsider don't have any effect).
The are a few guards who wear mask and goggles, probably to counter the effect of either dust storms or Howlers' hallucinogenic powder. Gameplay-wise, these don't actually have any protective effect.
The painting Serkonan Legends, Old Sea Beast is likely a depiction of a mythical creature called Devourer that roams the sea between the Empire and Pandyssia.
There is also a drawing by Emily (found in both Dishonored and Dishonored 2) which was done on a poster featuring a giant tentacled monster attacking a ship, likely depicting the same creature.
On the globes in Dishonored 2, there is another depiction of a giant sea monster with tentacles.
Serkonan Legends, Old Sea Beast.
Emily's drawings with possible depiction of the the Devourer in the background.
Another depiction of a giant tentacled monster found on the globes.
The book The Art of Dishonored 2 states that some people in Dust District believe there is something or someone that swings their shutters at night instead of the strong wind coming from the Wind Corridor. The painting Serkonan Legends, Knocker at the Window depicts this belief.
Each time you go back to the Dreaful Wale after a mission, new items from that mission are added to the interior of the ship.
After Addermire Institute: Hypatia moved into the storage, along with her equipment an a crate of Addermire Solutions.
After Clockwork Mansion: wall of light, arc pylon, and clockwork soldier parts can be found in the workshop.
After Royal Conservatory: an owl taxidermy and mounted head of a cerilope (a deer-like animal).
After Dust District/A Crack in the Slab: a few more Orbon Rum tanks are added to the briefing room. These were probably taken from the Crone's Hand Saloon as the Howlers seem to have an abundance of Orbon Rum.
At the beginning of The Grand Palace mission, Sokolov asks you to bring back some booze from the Duke's cellar. After this mission, many wine and liquor bottles can be found in the kitchen.
On a related note, it appears Sokolov has been working on some kind of device in the workshop. It can be found in the second mission, which means Sokolov started the project before he was abducted, and once he's back to the Dreadful Wale, you can clearly see the progress after each mission. I'm not sure what it is but it looks like a new type of arc pylon.
There are electrical boxes all around Karnaca that can be used to knock out NPCs. If you shoot or hit the panels, they will electrocute nearby people, or you can simply grab and throw someone at the panel. They actually remain active for a couple of minutes after being damaged so you can also use them as traps.
[Credit: superduper] Most of the photos of the targets on the briefing board are drawings, with the exception of:
Jindosh's - a silvergraph, the technology he invented.
Hypatia's - a newspaper cut-out.
The Crown Killer's - a wanted poster.
Many of the popular technologies and devices in the franchise have two versions, one in Dunwall and one in Karnaca. The devices in Dunwall are mainly manufactured by Sokolov Industries while those in Karnaca are mainly designed and manufactured by Jindosh Clockworks. This is not just the matter of design & aesthetic changes between Dishonored and Dishonored 2, since both versions of some devices can be found in Dishonored 2. In term of game development, in Dishonored the models of the devices in Dunwall were made with low-poly counts due to limited hardware capability at that time. But in Dishonored 2, instead of updating their models, Arkane chose to reused them thus making the game world more consistent, while making new distinctive models for Karnaca.
Two notable exceptions to this are the whale oil tank dispensers and refilling station. In Dishonored, Greaves Lightning Oil provided these equipment but in Dishonored 2 both Dunwall and Karnaca use dispensers and refilling stations manufactured by Jindosh Clockworks. After the Rat Plague, it's implied in the Return of Daud novel that Greaves Lightning Oil moved their HQs away from Dunwall so it's possible that they could no longer maintain the equipment.
Sokolov Industries' wall of light, displayed in the Royal Conservatory.
Jindosh Clockworks' wall of light.
Dunwall whale oil tank.
Karnaca whale oil tank, manufactured by Daiger-Dial Storage.
Dunwall loudspeaker.
Jindosh Clockworks' loudspeaker.
Sokolov Audiolog's audiograph player.
Jindosh Clockworks' audiograph player.
Dunwall arc pylon (only appeared in D1).
Jindosh Clockworks' arc pylon.
Dunwall alarm (only appeared in D1).
Jindosh Clockworks' alarm.
Dispenser and refilling station manufactured by Greaves Lightning Oil (only appeared in D1).
Jindosh Clockworks dispenser and refilling station.
The birds that fly around Karnaca bay actually have a very detailed model. [Credit: Zampo1it]
The book Traditional Serkonan Songs (1) has a song about a missing woman named Elmira. One of the verses mentions "she found a silver vein, longer than the Empire's reign". In the Dishonored Roleplaying Game, there is a bonecharm called Fragments of Elmira which whispers to the wearer in the voice of a woman and entices them to follow her directions to places where silver can be found. [Credit: Star.Gazing.Knight]
