Different Pokémon will possess different field abilities, and usually those of higher evolution stages will have higher intensities of that ability. For instance, a Torchic's Burn ability is at intensity 1, while that of Combusken's at 2, and that of Blaziken's at 3. After they clear the obstacle, they will depart from your team. Each obstacle can only be cleared by a single Pokémon, which means for an obstacle requiring 3 Burns, you can only use a Blaziken or other fire types with Burn x 3 to clear it. Using three Torchics, each with Burn x 1, will not do the job. If the Pokémon you use fails to clear the obstacle, let's say using a Torchic to clear a 3 Burn obstacle, Torchic will remain on your team, because in a sense it has not served its purpose. On the other hand, Pokémon with abilities at higher intensities may clear lower intensity obstacles, which means a Blaziken may clear an obstacle requiring 1 Burn, 2 Burns or 3 Burns. Note that Blaziken will still depart after clearing a 1 Burn obstacle or 2 Burn obstacle, because it has served its purpose in this case.

When you have cleared an obstacle, the obstacle will remain cleared the next time you visit, unless you challenge Entei, Raikou, and Suicune at the Fiore Temple and see the credits roll, which will reset all obstacles. So, in circumstances where you need to clear a series of obstacles to get to a certain Pokémon/place, once you've cleared one obstacle and discover that you don't have a Pokémon that clears the following, you don't have to bring a Pokémon that clears the first obstacle again the next time you visit. And exception to this obviously, is the Cross ability, which is required every time. To use a Pokémon's ability to clear an obstacle, simply click on the Pokémon, and drag a line towards the obstacle, the game will ask for comfirmation on using the Pokémon. Click yes to confirm, or no to change your option. For Pokémon that Charge, simply clicking on the Pokémon will trigger the question.

Obstacles List:

Obstacle Type	Description
Burn	There are various things in the game to be burnt away along your path, ranging from haystacks, metals or ice blocks.
Water	At the beginning of the game, you and your leader Hayate, will use Mudkips to put out fires on trees, but interesting that is the only time you will put this ability to this use. For the rest of the game, this ability is either used to grow plants for climbing or cooling off hot lava. It may also be used to wake Geodudes of Gravelers who may disguise themselves at ordinary rocks when they see you.
Charge	There are no obstacles requiring this, but it is one of the most important abilities in the game, since it is used for recharging your Capture Styler's HP, which goes down when it is attacked by Pokémon during capturing. Pokémon with Charge x 1 give 5 HP, those with Charge x 2 give 15, while those with x 3 fully recharge your Styler. Electric Pokémon are scattered throughout the game in various places, be sure to pick up a few before some major captures.
Break	Usually rocks or big boulders are required to be cleared by this ability, and the intensity ranges from 1 to 3. On certain occasions, this ability may be used to clear openings into caves.
Tackle	Tackle is mostly used for shaking trees (x 1) to find hidden Pokémon up there, or knocking down big trees (x 3) to create a bridge for river crossing. It is important for completing your Ranger Browser since some Pokémon may only be found on trees.
Cut	Obstacles that require Cut are usually fences or bushes, with intensities ranging from 1 to 2, and seldom 3. All of the sign posts may be destroyed by Cut x 1, but this doesn't seem to serve any purpose at all.
Gust	This is an ability used for unearthing hidden Pokémon more than actually clearing obstacles. Species like Oddish, Gloom, Vileplume, Parasect, and occasionally Lotad are buried in the ground when you see them. Depending on the intensity needed, you unearth them to challenge and capture them.
Cross	One of the important abilities for advancing in the game. It is also the only obstacle that requires clearing everytime (the others remain cleared until the end credits roll again), because the vine that helps you cross will not remain at the spot, and you must bring along a Pokémon with the ability when you visit the same place again. This obstacle/ability does not have intensities, it is always x 1.
Flash	A very minor ability that is only required once near the beginning of the game. Staryu is the only Pokémon in the game to possess this ability, and it is used to light up the store room in Prof. Shinbara's research lab. Its intensity is always x 1, and you don't really see this anymore later in the game.