Pokemon Found on Spikes
You get to ride a Rhyhorn ! How awesome! Head down to the Pokémon and interact with it to jump on. Start moving over the spikes. Spikes act like tall grass; so you can encounter Pokémon whilst moving through them. You'll eventually reach large rocks. Interact with them and Rhyhorn will break them.
Continue on through and move into the area without spikes on the ground. Break the rock there and dismount by pressing the B button . Head up the stairs and grab the X Defense . Remount your Rhyhorn and head back onto the spikes. Keep moving north.
When you see a clearing to the north-east, move over to that, break the rock there and once again dismount and collect the item. This time it's a Paralyze Heal . You can actually head east along the thin path to find a hidden Fire Stone . Nice!
Remount once more and head west, then north, breaking rocks as needed. Once you reach the next clearing, don't dismount just yet. Instead continue on to the one after that. When you reach it, break the rock blocking the stairs, dismount and head up them. Head around and grab the Dusk Ball here.
If you head up the stairs that lead to a point opposite a trainer, he'll ask you to partake in a Sky Battle . If you don't have any Flying-type Pokemon or Pokemon with the Levitate ability, you can't do one. Either way head back to your Rhyhorn and use it to head back to the previous clearing.
Talking to the woman here allows you to be healed, so do so. Remember to come back here whenever your Pokémon are running low on health. Head over to the cave and walk inside.
Tip #018: Don't Force Yourself In Sky Battles
Unlike typical trainer battles, Sky Battles are totally optional. If you don't have many strong Flying-type or Levitate Pokemon, it's often best to avoid them. There's nothing worse than getting wrecked with your vastly restricted team (or just one Pokemon) and losing some of your cash (plus ego).