NPCs Doing Things PCs Can’t
Sometimes, there is a concept for an NPC that just goes outside of the boundary of the rules. They do something that is impossible for the Player Characters to do, and sometimes this concept is a bit too powerful and can easily be abused if not carefully played. For example, maybe the concept is the NPC can control the flow of time at will nearly instantly. If a PC could have those powers there would be little I that could stop them. There are benefits to having impossible NPCs though, if you do it right.
First, the main villain cannot be this impossible NPC. They can be close to impossible, slightly toeing that edge and nearly breaking rules to make them into challenges to fight. But they cannot be the impossible ones because those are either impossible to fight or frustrating to run in combat. In fact, these are not NPCs that should be in a combat at all unless you have carefully thought through every round of what they are going to do.
These impossible concept NPCs are useful though. They represent something unique in the game world, a singular anomaly that does something that the players can’t. This can be used a tool to guide the players, or even reward them. For example, an NPC that is all knowing can give them information that would be otherwise impossible to gain. An NPC that shape reality can reward the PCs with new abilities or treasures. The problem comes when you are using the impossible NPCs for due ex machina, which is a poor practice and something to be avoided. These NPCs can’t swoop in and solve the conflict of the game with no warning or explanation.
You need to use them sparingly, but in powerful ways. If you downplay their abilities too much the concept is lost on the players. Sometimes, you don’t even need to have the NPCs be present in any of the sessions. These can be historical figures that left behind such great legacies that their influence is felt for hundreds if not thousands of years. A great wizard that rules over an empire they created through forgotten magic. A warrior that could never be killed and destroyed whole armies. A thief that stole the source of a nation’s power. The tales the players hear about them will only make things more poignant when they finally meet them or find a McGuffin connected to them.
Never be afraid to let your characters do impossible things. Be cautious, and use sparingly, but go ahead and use them. In literature, they are the legends and driving forces. Use them in the same way.