Click "Randomize (Save As...)". Save it as Pokemon Black 2 Randomized.nds . Load it in your emulator.
Do not just check every box. That creates an unplayable mess. Here is the "Expert Standard" setup:
This phenomenon has taken the community by storm, transforming a linear, predictable JRPG into a chaotic, endless replay value machine. If you have ever dreamed of starting your journey with a Mewtwo, fighting a Gym Leader who uses a team of legendary birds, or finding a wild Charizard in the tall grass of Unova, the randomizer is your gateway.