^

100% Requirements are:
-All 10 Power Berries
-All 7 Event Photos
-All 18 Fish
-All 27 Bugs
-All Plant Photos for the gender you're using
-All Farm Extensions
-Good Ending

The Farm Extensions cost a total of 180k g in the run, but you can get 30k for free by winning the Horse Races. You could trade a chicken to another cartridge and back again to make it golden, which sell for 10k g each, but that's banned, iirc.
We don't know the exact reqs. for the Good Ending, but I'm looking into it. If it has anything to do with GBC 1 & 3, it's most likely Happiness / # of Shipments / A few of each animal / Power Berries.

Edit: Good Ending reqs. are 10,000 total shipments, all 10 power berries, 70 happiness, 3 of each animal.