HMs are one of the core mechanics of Pokemon Diamond & Pearl that return in the remakes in a different form. In the original games, you could teach a Pokemon an HM, and they could use it to aid you on your adventure in the overworld.
In Pokemon Brilliant Diamond & Shining Pearl, you don't need to teach a specific Pokemon an HM to use its ability, so you can use the Fly ability outside of battle without any of your Pokemon learning it. Here's how you can get Fly in Pokemon BDSP, along with everything you should know about this useful ability.
Updated March 19, 2023: We've gone over this guide to make sure it's as accurate and readable as it can be, especially as Fly is one of the most important quality-of-life improvements you can get in a Pokemon game.
What Can You Do With Fly?
Fly is one of the most useful abilities you can receive on your Pokemon adventure because it allows you to revisit towns and cities that you've previously been to by calling upon a Pokemon to carry you from one location to another. Sinnoh is a big region, and each town has unique NPCs, so there are many reasons you may need to use Fly to return to a town quickly.
Unfortunately, you can't use Fly inside buildings or caves, so you can't use this ability to escape from an inside area that you wish to leave. Fly is an outside-exclusive ability.
You can use Fly through the Poketch, and a random Pokemon will carry you to any location you desire, so there's no reason to keep a Flying-type Pokemon in your party exclusively for the Fly ability.
How To Get Fly
Like other abilities in Pokemon Brilliant Diamond & Shining Pearl, you need to get the Fly HM and have permission to use it. This is a two-step process, so there are a few things you need to do before you can soar through the Sinnoh sky.
How To Earn Permission To Use Fly
Before you can use Fly, you need to unlock permission to use it by traveling to Veilstone City and defeating Maylene in a gym battle. Maylene is a powerful Fighting-type gym leader with three strong Pokemon in her party.
The first Pokemon Maylene uses is a Meditite, which is a dual Fighting/Psychic-type. Next, you'll face a Lucario, which you may know for its unique Fighting/Steel-type. The final Pokemon Maylene uses is a Machoke, which is a Fighting-type. You could bring a powerful Flying-type to counter Maylene's Fighting-type Pokemon, such as Staraptor.
Once you defeat Maylene, she will permit you to use Fly outside of combat.
How To Get Fly
After you defeat Maylene, you can travel to the northern side of Veilstone City to challenge a Team Galactic Base that appears as a Warehouse. There are a few Team Galactic Grunts you need to defeat before you can enter the building; however, they're much weaker than Maylene. When you enter the Warehouse, you'll find TM94, which contains the Fly ability.
You can now leave the Warehouse and start using Fly. This is a good time to return to previous locations to capture Pokemon and find items you didn't get the first time around.