Thought Dark Souls was too easy? Or perhaps too predictable upon your umpteenth playthrough? Well I've got just the thing for you, young grasshopper, as a modder JITD has tweaked the game to make enemies vastly more aggressive and unrelenting.
The mod doesn't actually influence enemies' health, damage dealt, or attack speed. That could jeopardise the delicate systems From tweaked to an insane degree. No, instead the mod makes it so enemies wander the map before you encounter them, effectively randomising their placement.
Furthermore, their line of sight is greatly improved, and they won't give up on chasing you, ever.
A side-effect of this mod is that it also makes NPCs prone to following you, which makes them harder to keep alive as they're essentially following the most wanted person in Lordran.
To see the mod in action, Dark Souls aficionado VaatiVidya made a video detailing the differences and suggesting tips like "skip Blighttown" and "running away doesn't work." (Also be sure to check out his "Prepare to Cry " videos on Dark Souls lore, if you haven't already.)
Go on and give it a go by downloading the Aggressive Mod from InsaneDifficulty.com.