So, since I've seen a few unique run ideas for Reborn aside from the standard monoruns, I figured I'd make a topic for people to discuss various different Reborn run ideas. Feel free to post some of your own or comment on run ideas. These runs don't nessesarily have to make the game harder, but can provide just a fun and interesting way to play Reborn.
One idea that I've had recently is a 'Red's Run'. You start with Charmander. You are free to use any Pokemon you come across up until you have six of Red's canon team Pokemon from any game, which is when you are only allowed to use them. Other 'Red's Teams' Pokemon can be obtained and be used interchangeably.
Red's cannon teams in every game he has appeared in (according to Bulbapedia) have seen - Pikachu, Espeon, Snorlax, Charizard, Venusaur, Blastoise, Lapras, Machamp, Arcanine, Meganium, Typhlosion, Feraligatr, Typhlosion, Jolteon, Scizor, Tauros, Raikou, Entei, Suicune, and Dragonite.
Optional Rule - Only Gen 1 Pokemon can be used prior to filling out Red's team.