When doing a superhero or science fiction type game it's always a challenge to come up with the mounds of villains ou need to be pounded. One solution I like is the hidden breed trope. Look, as an eample, how well Marvel has done with both their inhuman race and the mutant race of humanity. DC didn't do as good a job with their concept of "metahuman" but then they never really defined it well. On the third hand the wild card books did well with the wild card virus effectively creating a race of genetically enhanced super humans. The trick was even put to good use in Clive Barker's "Nightbreed."
For my purposes, I've come up with my version of this trope called simply the "New Breed." The New Breed are initially human and can't be told apart from humans with a DNA test. That's because the genetic information that sets them apart is hidden in the cells in nearly unbreakable spore like constructs. The very hidden nature of the New Breed plus that it only people born within a five year period (which years can be changed to suit the campaign) points to it being an artificial creation. But who created it? More importanly why? These questions can certainly be food for thought in any campaign.
Becoming truly one the New Breed requires death. It can be any sort of death as long as most of the head is there along with 50% of body. In this case, as soon as the person dies the sphores release the New Breed genes and infuse the DNA with a sort of pseudo life along the lines of a virus. Within one hour two unique organs are grown within the body connected by a string of nervous tissue. The first is in the chest opposite the heart. It's the size of plum and has been informally called "The Grand Shakra." It's working are a mystery still but it seems to gather virtual energy from the spongy quantum space that concerns much of string theory. The other organ is the size of a pearl and is formed under the hind brain. From it radiates two prongs that go from the hind brain to the frontal lobes. The tissue of this organ (dubbed "the Focus) is a combination of nerve tissue and dense pods that are filled with bacteria that seem to be acting as small computers. When both organs are formed there is a sudden rebirth and the New Breed starts life again. Generally, they are regenerated back to their own previous self though without any chronic health conditions. I say generally because there is a random component that happens because the whole New Breed program was ultimately a failure. The New Breed should be able to manipulate reality and do practically anything. Unfortunately, this was the equivalent of strapping space shuttle engines onto a gremlin and going for a spin. Humanity just can't handle the power and so as a defense mechanism it tends to shut down a huge part of the potential of being a New Breed. Don't get me wrong, the New Breed like marvel mutants are extremely powerful beings they just don't live up to their potential.
One example of the New Breed and a good way to introduce the New Breed to the campaign is Mercy. Mercy was killed and left for dead in Central Park by a mugger. When he arose he was acutely aware of his own death and new self to a degree that profoundly shook his sanity. He immediately tried to kill himself. And failed. His powers includes a truly incredible regenerative ability. He's harder to kill than a story about the Kardashians. He might have checked into a mental institution to help with his profound depression except his other power kicked in at that point. Unlike modern science Mercy can sense the New Breed before they die and enter the new stage of their lives. This ability is not perfect being that he gets a false positive result about one third of the time. Still that's two thirds of the time where he has the ability to bring a person to his ultimate ability to the world. This has filled him with a mission. He will awaken all the New Breed he can and if dull humans die then so be it. Mercy has become an extremely dangerous serial killer. It would be a good introduction to the entire concept if Mercy gets a vibe off a friend of someone in the campaign and then targets them. Trying to stop a nearly unkillable killer would definitely provide a challenge and if he does succeed then the Game Master has two interesting choices. Either Mercy was wrong and the friend is now dead and the hero is going to have to deal with that lose, or suddenly hero's friend is now a superhuman being and the hero is going to have to deal with the new state his friend is in. In either case it's good drama.