Walkthrough: After defeating your first Island Trial, you can return back to Verdant Cavern to catch the Wild Pokemon found within or collect any items you may have missed.
Wild Pokemon:
Standard Walking (Levels 8-11) Zubat(70%), Diglett(30%)
Rustling Spots (Level 11): Yungoos(100%)
Zygarde Cells: There is one Zygarde Cell found in the Cavern.
Items:
Super Potion - Southeast of Cave
X Defense - Northwest of Cave
Super Potion - In Hole In Northeast of Cave
Revive - In Front of Big Rock Before Ramp (Hidden)
TM31 Brick Break - Southwest Ledge of Cave
TM46 Thief (Totem's Den) - Hill Above Pedestal
Great Ball x10 (Totem's Den) - From Ilima After Defeating Trial