"An ancient sapphire ring.
It subdues your presence, making it difficult to be detected by enemies."
The description for the Thief's Ring in Demon's Souls is innocuous enough, but it's one of the most useful items in the game.
When I first obtained it, I scoffed at its effects. I generally tend to be underwhelmed by "ancient and powerful artifacts" that serve as nothing more than marginal stat modifiers. I also wasn't playing a stealthy character, so it seemed like a fairly useless trinket.
Demon's Souls is a game where a small boost can have an enormous effect, though, and a few deaths later I quickly discovered the benefits of donning the Thief's Ring.
There's nothing magical about it, really -- it simply does what it says -- but its effects are very deliberately tied into the game world and its design.
Here a few examples:
Unlike many 3rd person brawlers, the enemies in Demon's Souls do not patiently wait for their turn to attack the player. As a result, it's often important to draw away individuals from a group to take them on one-on-one.
The Thief's Ring facilitates luring enemies by preventing the player from being pelted with projectiles during the approach. What's more, the combat in Demon's Souls requires a lot of movement, and the Thief's Ring makes it less likely to draw the attention of more enemies while battling a solitary opponent.
The ramparts of Castle Boletaria are patrolled by hostile dragons that roast anything in their sights. These sections are quite unforgiving, but the Thief's Ring expands the window of safety between the dragons' fiery onslaughts.
Crystal Geckos are timid creatures that are almost impossible to catch with a melee attack. They can spot the player from very far away, and if they do, they skitter back and fade out of existence. The Thief's Ring slightly dulls their awareness, making it easier to catch them and the large quantities of minerals (used to upgrade armour and weapons) that they drop.
Chances are that during most everyone's first playthrough at least a few of the boss battles will not end in victory, but the Thief's Ring makes it easier to give 'em another shot. Simply running past enemies is often a valid option, and equipping the ring lowers the duration/distance they'll take into account when chasing the player.
Upon defeating a boss, the player can warp back to the boss' lair from the Nexus hub. This not only provides a shortcut going forward, but it also allows the player to go back through a completed area in order to obtain more items and souls (the game's equivalent of gold and experience).
What makes this backtracking different from playing through the same area from the start is that enemies tend to face only one direction. Combined with the Thief's Ring, this makes it quite easy to sneak up on them and unleash a backstab, a special attack that deals extra damage and yields more souls.
Equipping the Thief's Ring is practically the only way to travel up narrow mountain paths without being shredded by flying Storm Beasts.
The blind boss of the Adjudicator Archstone is quite a fearsome opponent, but it's actually quite easy to stay out of his reach with the Thief's Ring equipped.
Player vs. Player combat is not greatly affected by the Thief's Ring, but it does partially obscure the invader. This makes it more likely that the battle might begin with a sneaky backstab.
Even without any significant gameplay mutators, though, it's still quite unsettling to see a swirling, red aura make a beeline for the player's character.