Bad difficulty basically comes in the game throwing "challenges" in ways the player has no potential to address or mitigate.
Mostly this comes in the form of poorly done RNG systems where winning is a toss-up dice roll. You have to roll good loot to possibly win, or hope that the enemy doesn't randomly pick its "Game Over" attack out of its moveset. There are lots of games that use RNG, but the good ones always use tweaks to avoid stupid unwinnable situations. Even in games that don't seem dice-based, this can come up with lazy AI if its given random actions.
Another commonplace one is Interface Screw. This can range from poor design to begin with, including awful camera controls or button layouts. It can also be invoked deliberately by locking the camera in an unfavorable position (some third person action games will have boss fights where stuff is actually spawning offscreen behind you where you can't see it, for instance), weird meta attacks that alter your controls, or more simplistic things like simply hiding enemies in ambush points where you can't possibly aim the camera to ever see them (alongside no indicators of the ambush).
Thirdly, there's inconsistent physics or mechanics. A certain degree of that can be waived off as balancing a dumb AI against a human, but there's definitely games that go overboard. Enemies that never have to reload their guns (or Skyrim's infinite mana enemy mages), the infamous Souls "magic homing arrow that clips through walls", AI's in strategy games who don't even bother to collect resources, enemies that can see through walls or react to your button inputs. A fall being safe in one instance, then lethal in another despite being an identical distance.
As the pausing of Dark Souls goes, I wouldn't consider it relevant to the difficulty, but it does seem an arbitrary and annoying restriction. If I'm playing offline (which the game allows), I don't want to deal with having to restart a 10 (or more) minute boss fight because my phone rang, or my dog needed out, I spilt a drink, etc. It doesn't alter the actual gameplay or mechanics.
Mostly this comes in the form of poorly done RNG systems where winning is a toss-up dice roll. You have to roll good loot to possibly win, or hope that the enemy doesn't randomly pick its "Game Over" attack out of its moveset. There are lots of games that use RNG, but the good ones always use tweaks to avoid stupid unwinnable situations. Even in games that don't seem dice-based, this can come up with lazy AI if its given random actions.
Another commonplace one is Interface Screw. This can range from poor design to begin with, including awful camera controls or button layouts. It can also be invoked deliberately by locking the camera in an unfavorable position (some third person action games will have boss fights where stuff is actually spawning offscreen behind you where you can't see it, for instance), weird meta attacks that alter your controls, or more simplistic things like simply hiding enemies in ambush points where you can't possibly aim the camera to ever see them (alongside no indicators of the ambush).
Thirdly, there's inconsistent physics or mechanics. A certain degree of that can be waived off as balancing a dumb AI against a human, but there's definitely games that go overboard. Enemies that never have to reload their guns (or Skyrim's infinite mana enemy mages), the infamous Souls "magic homing arrow that clips through walls", AI's in strategy games who don't even bother to collect resources, enemies that can see through walls or react to your button inputs. A fall being safe in one instance, then lethal in another despite being an identical distance.
As the pausing of Dark Souls goes, I wouldn't consider it relevant to the difficulty, but it does seem an arbitrary and annoying restriction. If I'm playing offline (which the game allows), I don't want to deal with having to restart a 10 (or more) minute boss fight because my phone rang, or my dog needed out, I spilt a drink, etc. It doesn't alter the actual gameplay or mechanics.