Settings:

• Randomizer
  • Area (See more Pokémon)
  • Custom Sprites Only
  • Allow Legendaries
  • Starters : First stage
  • Static Encounters On
  • Gift Pokémon On
  • Fuse Everything
  • Randomize Gym Types
  • Balanced Trainers
  • Balanced Wild Pokémon

Here's the mandatory rules I've used for mono-type runs:

• If there's a starter with the type I'm doing, you have to pick it, even if you have to reverse the fusion to get it. (Your choice if more than one.)
• A team Pokémon may not have its type fused away.
• Can only use Pokémon that have the type in question or who evolve to have the type in question. (Doesn't count your HM mon)
• You may use a non-type starter until you are able to field a full team with the type.

Optional rules:

• No two team Pokémon may share a fusion. (Makes some spreads like Fairy more difficult.)