Holon Grasslands
The Holon Grasslands is north of Settlement Foxtrot and west of Settlement Oscar.
Pokemon in the grass include Sceptile (lv 80-82?), Mawile(lv 78?), Escavalier (lv 79-80?), and Unfezant (lv 78-80?).
Pokemon found while surfing include Clawitzer (lv 80?).
Delta Mawile can be found in a hidden grotto north of the Heart Swap statue (to the west of the Painter).
Delta Treecko can be summoned via a sign on the northern edge of the map ('START BUZZER'). If you move the Heart Swap statue into its path, it will stop and can be battled.
North of the Rich Boy there is an upright log which gives the message 'It's an old, mystical tree trunk' when interacted with. Perhaps this is where you encounter Delta Petilil (Fairy)?
In the northeast there is a flower patch where you can encounter a Combee.
There is a Rare Candy hidden behind a tree on the left side of the flower patch.
There is an Ultra Ball behind a tree north of the Rich Boy.
TM89 U-Turn is hidden behind the right side of the cracked rock.