Hidden Moves (HM) are, well, Pokémon moves that have their uses outside of battle. In the original Diamond and Pearl, you needed to teach HMs to Pokémon that can learn them in order to use the move.
However, Brilliant Diamond and Shining Pearl stores most of them into the Pokétch, so you don't need to permanently have Bibarel in your sixth team slot. The Hidden Moves Pokétch app lets you call nearby Pokémon that know the move (read: Bidoof and Bibarel) to assist you around the overworld.
Here's where to find all important HMs, including some that don’t get added to your Pokétch in Brilliant Diamond and Shining Pearl.
How to get Rock Smash
Rock Smash is automatically obtained once you enter Oreburgh Cave. The Hiker near the entrance will give it to you.
You can use Rock Smash outside of battle after you defeat the Oreburgh Gym Leader. As its name implies, it will let you smash small rocks.
How to get Cut
Cut is automatically obtained in Eterna City. Cynthia will give it to you. You can use Cut outside of battle after you defeat the Eterna Gym Leader. It will let you cut down trees.
How to get Flash
Flash can be found in the Oreburgh Cave. Climb down the stairs and hop down one of the ledges on the right. It’s inside a Pokéball.
Flash is not added to the Pokétch. You need to teach a Pokémon the move and use it from the Pokémon menu. It lights up dark caves.
How to get Strength
Strength can be received from the Old Lady in the Lost Tower south of Solaceon Town. You need to climb the top floor to reach her.
You can only use Strength outside of battle much later into the game, after you defeat the Canalave Gym Leader. It will let you push boulders around.
How to get Fly
Fly is found in a Pokéball in Team Galactic’s Warehouse in Veilstone City. You can enter it as soon as you defeat the Grunts guarding the entrance together with Dawn or Lucas.
You can use Fly outside of battle after you defeat the Veilstone Gym Leader. It will let you fast travel to any city or town.
How to get Defog
Defog is given to you by an Ace Trainer in the Safari Zone at Pastoria City. You can find her near the entrance.
You can use Defog outside of battle after you defeat the Pastoria Gym Leader. It will clear foggy Routes for you.
How to get Surf
Surf is automatically obtained in Celestic Town. Cynthia’s grandmother will give it to you after you look at the ancient cave painting.
You can use Surf outside of battle after you defeat the Hearthome Gym Leader. It will let you travel on water.
How to get Rock Climb
Rock Climb can be found in Route 217. It’s inside a Pokéball located at the back of the lone house in the area.
You can use Rock Climb outside of battle after you defeat the Snowpoint Gym Leader. It will let you, well, scale up climbable rocks.
How to get Waterfall
Waterfall can be obtained by speaking to Jasmine in Sunyshore City after you defeat the Sunyshore Gym Leader. She’s located just north of the Sunyshore Market. The hidden move will let you go up waterfalls, allowing you to enter the Victory Road and challenge the Elite Four.
How to get Sweet Scent
Sweet Scent is not available as a TM in the game, so you will need to catch a Pokémon that knows the move if you want to use it, like Roselia and Combee.
Much like Flash, you need to access the Pokémon menu to use sweet scent. It will let you encounter a wild Pokémon, even with Repel active.
For more help with Pokémon Brilliant Diamond and Shining Pearl, we at Pro Game Guides have you covered.