As you journey through the Kanto Region, you will come across Pokemon that must be interacted with in order to go into battle against them. Otherwise, even though found in the Wild, you will be able to battle these Pokemon and possibly capture them. In all, there are four different Pokemon that can be interacted with during your adventure, two of which you will need a special item in order to do so.
Available Interactable Pokemon
Snorlax: The first two interactable are none other than Snorlax, with one blocking the path on Route 12 and the other doing the same on Route 16. You will need the Poke Flute in order to interact with the Snorlax, which is obtained from Mr. Fuji after saving him from Pokemon Tower. Both Snorlax will be at Level 30.
Electrode: Throughout the Power Plant, you will find what look like Poke Ball Items that will actually turn out to be Pokemon. Once interacted with, these Pokemon will attack and turn out to be Electrode. All of them will be at Level 34.
Hypno: During your mini adventure of the Sevii Islands after defeating the Cinnabar Island Gym, you will have to save Lostelle from Berry Forest on Three Island. Once you find Lostelle, the Pokemon that kidnapped her will attack. It will turn out to be a Hypno, the same that will be at Level 30.