Decomposing Corpses.

When someone dies you have the option to bury them, in which a small grave mound will appear.
Alternatively if you do nothing the corpse will stay in the position it was and bloat, shrivel up, and after a long enough time turn almost fully into a skeleton. The length from start to final decomposition is about 30 days. Decomposing unburied corpses sour the mood of the rest of the NPCs and increase chances of disease.

Stealing Owned Goods.

Some goods have an owner associated with them, either a faction or specific NPC. If stealing from a specific NPC the game will look if the NPC has a faction associated with him. When you pick up an item your player character momentarily has a tag labeled 'stealing' for a few seconds, if an NPC if the faction you are stealing from happens to be looking at you, you will be attacked by all NPCs of that faction and have a soured relationship with said faction, and NPC owner if they exist.

Wall Crawling Monsters.

Monster characters can crawl on walls. This could be accomplished by having a floating pawn movement along with character movement; Character movement component gets disabled when Floating Pawn movement component is enabled. Then the character swivels head around, casting a short ray trace from their eyes, if they hit a wall object, they go close as they can to the wall object, facing the wall object, and then initiate a crawling animation and move up a little bit continously casting a short ray from their abdomen to readjust to the curvature of the wall if there is one, while moving in randomized directions at the same time.