Unconventional playthrough rules?

What's a unique rule you used for at least one playthrough of a Pokemon game? This can be anything, from an entire challenge run to just a special rule you set for yourself for that particular run.

I personally have done a mono-Water playthrough of Y and mono-Flying playthrough of Ultra Sun, but I also did a playthrough of Violet where I use both Water and Flying types but don't catch any other types.

I also have an unfinished playthrough of Ultra Sun where I use Nuzlocke catching rules- I only catch the first Pokemon on each route, except for one team member I really wanted to use.