When the membrane between other shards of the multiverse grow thin, worlds that occupy the same space can overlap, especially where there are concentrations of potential on both sides of the divide. When this concentration exists in a living thing, reality cannot consolidate the discrepancy, and a Nemesis is born as a result. They relentlessly attack whoever they have copied, while their target has every ounce of potential in their being to defend themselves. If the nemesis wins, it takes their place, lashing out against its new home. If the native target wins, they get to keep the mass of energies reaped from the rift.