The developers have put a lot of thought into what a player might do (variety of entry routes, violent to pacifist runs, etc), yet a lot of things they didn't consider (deflecting missiles with wind, "I just made a level designer cry!" platforming, etc) are still mechanically possible. However, a fair number of very interesting things can happen, given the circumstances:
- Try throwing something (or shooting) at a Wall of Light just as a guard is walking through it. Doing so will cause the Wall of Light to do some Friendly Fire.
- Early in the game, you will be asked to go into the tavern's sewer system to deal with a couple of weepers. Admiral Havelock gives you the key to access the area. By possessing a fish, you can access the sewers by swimming between the bars of the seaside grate and eliminate the weepers without ever being asked to or being given the key. This won't net you any additional dialogue, but what shows the developers thought of this scenario is that you'll find another key to the basement inside the locked door when you try to leave.
- During the mission to neutralize Campbell, pretty much any possible outcome is accounted for, up to and including you preemptively stealing the Solokov painting in Campbell's secret room before he leads Curnow down there which itself only happens if you smash both wineglasses. Additionally, Curnow will attack you if you show yourself at any point during the mission. Unless you smash both wineglasses, follow the two down to the secret room, remain unseen, and wait until Campbell draws his sword to kill Curnow before you take Campbell down. If all of those conditions are met, Curnow will acknowledge that you have saved his life, and instead choose to look the other way and flee the compound rather than alert the Overseers to your presence. Even the official guide doesn't mention this.
- Furthermore, if you switch the wineglasses, then possess Campbell after he drinks which is only possible if you collect every rune available up to that point and spend them all on Possession then you will get a Non Standard Game Over stating that you have been poisoned.
- On the topic of Campbell's portrait, it's supposed to depict Campbell posing beside a table with a bottle of brandy on it. When you pass by Sokolov and Campbell during the game's prologue, drinking the brandy will earn you a snarky comment from Sokolov... as well as causing the bottle to be missing from the portrait when you collect it later.
- If you empty Art Dealer Bunting's safe before giving the combination to Slackjaw (who plans to do the same), the latter will call you a "cheater" next time you meet him. This does not seem to happen if you close the safe again and set the numbers back to 0, though, something few players would ever think of doing.
- If you join any of the Lady Boyles when they use the toilet, they will have specific lines for that scenario. All of them are a variation of "Are you serious?"
- The Boyle mission includes the ability to find a portrait cameo worth a lot of coin. Its easy to miss for players that don't know its there, isn't required for the mission, and is only briefly mentioned with little indication as to where to find it. But finding it helps prep the player for the Granny Rags fight.
- The Boyle Party involves the player having to gather clues to determine which of the three Boyles is his target. This is randomised each time the mission is played. When the player has enough evidence, the objective tracker will change to reflect this, changing from telling the player to identify his target to telling him to eliminate her. But if the player simply kills all three women without determining which of the three is his target, the objective tracker will state that the objective was completed by "process of elimination".
- Daud's final comment will be altered if Corvo wanders off before Daud actually finishes talking, or if Corvo walks away entirely after Daud's speech concludes. Additionally, if you spare said character with Low Chaos, their guards are no longer be hostile toward Corvo and will let him walk around freely.Daud: ...Unexpected.
- Should the player backtrack to the gatehouse at Lady Boyle's party and eat the apple in front of the guard, he will comment "My apple! Who do you think you are?" CORVO!
- In a high chaos run of the last mission, Pendleton is trapped in Martin's siege of Kingsparrow Island. They provoke each other until Martin pulls out his gun and goes for a shot. There are several ways for this scene to end:
- Straight through the script: Martin misses his shot, is further provoked by Pendleton, and moves up to his quarters to devise a plan on how to get to him.
- While hidden, you shoot and kill Pendleton before Martin fires his gun, surprising him and causing him to ask around who made the shot.
- You make your presence known by shooting and killing Pendleton while out in the open (or by going to his hiding place to execute him there), wherein Martin will acknowledge your presence.
- You shoot and kill Martin before he leaves, wherein Pendleton will congratulate you on dispatching him and then immediately offer a bounty on your head.
- You shoot Pendleton in the head and kill him at the same time Martin would miss with his shot, wherein Martin will say "Nice shot!"
- In the last mission on high Chaos, at the very end, Havelock holds Emily hostage on a ledge. You can obviously just shoot him and save Emily, sneak around and kill him, but it's also possible to simply run into him; he'll fall, taking Emily with him, but Corvo will reach out and grab her and pull her to safety.
- In the same scene, it's possible to use Possession on Havelock. Once in control of him, Corvo will release Emily, who will recognize him, ask if he's using magic, and flee the scene. Unpossessing Havelock then allows the player to fight him as they would in a low chaos run.
- When you're introduced to the Hounds Pit Pub, should you decide to first enter the place by climbing through the servant room window (it must be your first ever time entering the building, though the bar doesn't count), it'll trigger some unique dialogue from Lydia as you startle her.
- Late in the second mission, it is possible to find three Overseers and a woman arguing. One will be trying to defend the woman, who is his sister, while the others believe she's a witch and are attempting to kill her. If you let the scene play out, both the woman and the defending Overseer will be killed. If you attempt to intervene before they've finished talking, all three Overseers will turn on you because there was no immediate danger. If you intervene after they've finished talking, disable both attacking Overseers, but manage to keep the defending Overseer and his sister alive, they'll thank you and reward you with a nearby safe combination.
- During the first two missions, both Granny Rags and Slackjaw will request you retrieve an object from Doctor Galvani's Office. You can actually visit Galvani's house and retrieve said object before speaking to either of them. If you do, Granny Rags and Slackjaw will acknowledge that you've done so.
- Tallboys. Most players, when handed a stealth game, immediately move to the highest places possible to significantly reduce the chances of being spotted by guards and the like. Tallboys take away this advantage, as their metal legs put their field of vision level with most mid-height climbable features, plus they look down into low cover. You have to get way above them to sneak past, but then forward movement becomes much more difficult.
- Any player going for a non-lethal run might discover the hard way that, if you place an unconscious guard on a set of stairs, they will slide down and hit their head at the bottom if oriented head-down, and this can kill them.
Brigmore Witches DLC
- In the final room of the game, you have the option to non-lethally neutralize Delilah by swapping her painting with one that will seal her in the Void. Before starting her ritual, she will turn away from her work, but turn back to it for a moment. If the player swaps the paintings during this window, Delilah will notice and immediately twig that Daud is on to her, causing her to start hunting him.
- In the sewers during the Dead Eels mission, you encounter a witch pretending to be injured. If you confront her directly, an ambush will happen. However, if you take a detour and find the two witches hiding nearby, Daud will have the option to torture the witch instead, citing that he already knew what the witch was up to.
- While in Dead Eel territory, there are two places where one of your assassins will drop by to give you information. They'll have a line where they talk about a feeling of being watched. If you can find and neutralize the witch spying on the Dead Eels before triggering this dialogue, they won't mention that feeling.