Like all of these games, Omega Ruby and Alpha Sapphire have their fair share of interactable Pokemon. These are Pokemon that can be seen and talked to via the map, but are not legendary status.
Location: New Mauville
Hidden in New Mauville, there are various PokéBalls on the ground. Some of them are items, while others will activate and attack you, as they are Voltorb.
Location: Route 119, Route 120, Lavaridge Town, Mossdeep City
As you progress through the game, you will get blocked by Kecleon on the bridge on Route 120. Using the Devon Scope, you can awaken it and it will attack you. There's two more in Route 120, one in the plant maze and another blocking the stairs down to the Scorched Slab. There's also one in Route 119 blocking an Acro Bike bridge
After you have beaten Primal Groudon/Kyogre, two more Kecleon are found. One in the hot springs in Lavaridge Town, and another in Mossdeep City's Space Center after the Delta Episode. The one in Mossdeep City has its Hidden Ability
Location: Magma Hideout, Aqua Hideout
Hidden in the Magma Hideout and the Aqua Hideout, there are various PokéBalls on the ground. Some of them are items, while others will activate and attack you, as they are Electrode.
Location: Sea Mauville
After you have confronted Primal Groudon/Kyogre, when you get to Room 4 in Sea Mauville, you will hear of a presence like you're being watched. If you check the top left bookcase, you will learn that the Odd Keystone was lost on Sea Mauville, and then get another note about being watch. Then, if you select a menu option such as Items, Pokédex etc., then when you exit, the Odd Keystone will be behind you and Spiritomb will attack.