|Marill||Water||Surf||30%, 60% (Rippling)|
|Red Basculin||Water||Surf/Super Rod||70% (Surf), 35% (Rippling), 30% (Fishing)|
|Blue Basculin||Water||Surf/Super Rod||70% (Surf), 35% (Rippling), 30% (Fishing)|
|Goldeen||Water||Super Rod||70%, 60% (Rippling)|
|Seaking||Water||Super Rod||10% (Rippling)|
To begin with, head south towards the stairs and take on the Ace Trainer here.
Trainer Battle: Ace Trainer
Continue west up the stairs. Head north through the Tall Grass when you reach the top. Continue past the steps leading west until you reach the end. In the north-east corner there is a tile that oddly doesn't contain Tall Grass. It instead contains a hidden Carbos though. Grab it, using the Dowsing MCHN to find it if you need.
Head back south and head down those steps leading west. Now head south down to the steps to your west taking you north up onto the elevated area. Move over and challenge the Backpacker here.
Trainer Battle: Backpacker
Head down the steps to your west. Now move north and head east into the Dark Grass north of the elevated area you were just on. Keep heading east until you find the Amoonguss posing as an item in the grass. Feel free to take it on if you want.
Wild Pokemon Battle
Head back west and move to the north-east corner of the Dark Grass patch. There you'll find a PP Up . Head back out of the Dark Grass and move back to the stairs. This time move up the stairs leading west. If you've beaten Marlon, Terrakion --another of the Legendary Musketeers--will suddenly appear nearby.
Colress will also come from the east! After you answer a question (it doesn't matter what answer you give), you'll be given the peculiar Colress MCHN . Hmm, could this be what Colress used to move the Crustle blocking the road earlier in the game? Colress will then leave and you'll be free to face Terrakion or continue exploring.
Reminder : Remember to Save before checking out Terrakion! You only get two chances to snag this bad boy.
Legendary Pokemon Battle
As before, you don't have to battle Terrakion, but it's recommended. You may especially want to consider catching it as it'd be a worthy addition to your collection. By now you should have encountered two Musketeers already, so you ought to have enough Legendary-catching experience.
Before committing yourself to the battle, check you have plenty of good Poke Balls (Ultra Balls, Timer Balls, Dusk Balls) and that your Pokemon are fit and ready for battle.
Unlike Cobalion and Virizion, Terrakion has beastly Attack and can do a massive number on your Pokemon with Rock Slide or Sacred Sword. Ghost Pokemon will take no damage from Sacred Sword, but Rock Slide will still hurt. Ground- and Fighting-types meanwhile will take half damage from Rock Slide.
If you can inflict Paralysis, for example with Thunder Wave (purchased from Nimbasa City's Pokemon Centre), that will occasionally stop it hammering your Pokemon, as well as boosting your catch rate. Moves like Reflect or Charm are also useful to lower its damage output.
Should the worst case scenario occur--you forgot to Save your game and accidentally faint Terrakion, you can encounter it again, but only after youve beaten the Elite Four. Which isn't too far away, we suppose. In that event, Terrakion will be Level 65 instead of 45.
Once youre done, move up the ramp onto the thin walkway. Now purposely drop down into the Dark Grass below and grab the Rare Candy on the west side of the area. Move south-east, toward the ledge you can jump over to get back to where you were. Just before the ledge is a Hiker who wants to battle with somebody.
Trainer Battle: Hiker
Jump over the ledge and move up the ramp onto the thin walkway to your east. Circle around and move west off the ramp to the north of where you moved onto the walkway. You'll be on an elevated section. Use your Dowsing MCHN to find the hidden Green Shard then move back onto the walkway and follow it east.
When it turns south, continue to follow it and move down onto the area below. Take on the Pokemon Breeder!
Trainer Battle: Pokemon Breeder
Note: Like most Pokemon Breeders, he will challenge you to a battle if you move in front of him any time after you leave and re-enter this area.
Now use Strength to push the nearby boulder into the hole. If you need to head back to Humilau City to heal, we'd recommend doing it now when you have the shortcut back. Once you're ready, use Surf on the water to the Breeder's south. Head down the pond until you reach the western shore.
Move onto the shore and move left behind the trees. There's an obscured Calcium tucked away here. Grab it then Surf back to the other shore. Now use the thin walkways to head all the way back to the Terrakion. Now head south from the Terrakion through the Tall Grass.
When you reach the two sets of stairs, continue south past them and grab the Poison Barb . Now head down the western set of stairs, then head north and head down a second set of stairs leading west. Move north up the side of the Tall Grass here.
Just before you reach the Backpacker, look for the item in the Tall Grass to your west. It's actually an Amoonguss , but feel free to battle it if you want. There'll be an actual item to your south-west. Move over and grab it, a Red Shard . Move back north-west. You'll find a male Backpacker looking for a battle.
Trainer Battle: Backpacker
Circumvent the Tall Grass by moving counter-clockwise around it. You'll see an entrance to a cave known as the Giant Chasm. You can head in there now, if you want, but let's keep heading south first. You'll eventually reach an Ace Trainer. Move up to her and battle her.
Trainer Battle: Ace Trainer
Move up the steps leading east to her south. Now move along the walkway taking you north. Take the path leading directly north and follow it until you reach the end. Move down onto the ground and grab the Max Potion . Now move onto the walkway and drop down to the ground below.
You've done everything! If you want, you can head over to the entrance to the Giant Chasm and go inside. But until you've used the Colress MCHN to explore Seaside Cave you won't be able to progress further in. If that's the case, let's first head to Route 21 towards Seaside Cave then!