Been obsessively tracking this niche for years, ever since a certain FFN author wrote 'The Other Veil' back in the day—long gone, sadly. The premise that sticks is when Harry's MoD status interacts with Twilight's immortal physiology. Most fics treat the Master of Death like a cosmic admin pass; he can't truly die, which forces a weird tension with Edward's mind-reading or the Volturi's threat assessment. A lot of authors get stuck on power-leveling, making Harry an unstoppable force that just lectures the Cullens.
But the ones that linger focus on the loneliness. There's a short, unfinished piece where Harry, after centuries, wanders into Forks not for a fight, but because he's drawn to another 'frozen' creature. He and Edward don't become friends—they just sit in silence, two different kinds of eternal. His power isn't about wands, but about seeing death in everyone, including the sparkly 'immortals'. The magic system rarely meshes well, but the character study can be sharp if the writer avoids turning it into a crossover curb-stomp.