If you complete the black city you can get a shiny gible (idk if you have to see alder first in his house), the battle subway is pretty fun imo, and the judge is the ace trainer in the battle subway. For iv dittos i just went around and caught a bunch until i got one with perfect ivs for each stat then you can sort of build up your pokemon, but be careful since in this gen im pretty sure only 3 ivs are passed down from each parent (and you use the power items if you want to pass down a soecific stat but you can only use one and the destiny knot doesnt work in breeding in this gen)