In Pokémon HeartGold & SoulSilver, there are only 3 ways to get Black Sludge:
- You can find a single Black Sludge on the ground deep inside Cerulean Cave after earning all of the Kanto Gym Badges. (Once-only)
- You can also infinitely farm Black Sludges by using a clever combination of moves to steal from Elite Four Koga’s Muk. (Repeatable)
- Or if you’re in the early-game before clearing all the Kanto gyms, wild Croagunk in the Safari Zone’s Marshland Area have a 5% chance of holding Black Sludge – but you’ll need to place 42 forest blocks before they appear. (Repeatable)
Poison-Type Pokémon holding a Black Sludge will regenerate 1/16th of their maximum HP at the end of every turn, much like Leftovers.
If the Pokémon holding the Black Sludge isn’t Poison-Type, they’ll take 1/8th of their maximum health as damage each turn instead of healing – so you can also use item-switching moves like Trick or Switcheroo to weaponize your sludge.
We’ll run through all of the methods of getting a Black Sludge below.
Method 1: The Black Sludge Hidden in Cerulean Cave
To find the only Black Sludge hidden in the overworld, you’ll first have to earn all 16 Gym Badges.
Once you’ve done that, head to Cerulean City.
You’ll need to bring a Pokémon with Surf, plus a Pokémon with Flash if you want to see once you’re inside the cave. It may also be a good idea to bring a Pokémon with Dig or an Escape Rope because you’ll be traveling deep into the cave.
Finally, Cerulean Cave contains the toughest wild Pokémon in the game – so bring a strong team or plenty of Repels.
Once you’ve arrived in Cerulean City, take the north exit onto Route 24.
Cross the golden bridge onto Route 25, then take an immediate left once the bridge ends and walk down the stairs.
At the bottom of the stairs, use Surf on the water at the point pictured below.
From here, Surf directly down south as far as you can go and follow the river round to the left.
You’ll soon come to the entrance of Cerulean Cave. If you’ve successfully collected all 8 Kanto Badges, there should be nobody blocking the entrance.
Head inside and use Flash to illuminate your surroundings.
Once you’ve lit up the cave, walk straight forward and Surf on the first body of water you encounter.
Surf straight up north and take the first left turn you encounter.
Follow this stretch of river as far to the left as you can, then head down south until you reach the first set of stairs, pictured below. Disembark here.
From here, take the path going south.
Follow this one-way path around for a while until you reach a ladder at the top of a steep staircase, as pictured below.
Climb the ladder and you’ll emerge into an intimidating-looking crystal maze.
Don’t worry though, the path is easier than it seems. Simply take the north option at the first fork you come to.
Shortly after that turn, you’ll come to a second fork. Take the right option.
After that, it’s as simple as following the remaining one-way path until you reach some stairs and a ladder going down a floor. Climb down the ladder.
When you climb down the ladder, you’ll find yourself in a small room with another ladder leading deeper into the cave. Climb down this one too.
On the next floor down, follow the one-way path to the north until you reach the intersection pictured below – take the second right turn.
Follow this path until you reach a body of water. Surf on it.
Surf to the right and then up directly north.
Before long, you should reach the small shore pictured below. Disembark here.
Once you’re on dry land, take the path up north. Follow the bend round and back down south until you come to another patch of water. Surf here.
Surf down south and take the second right turn, pictured below.
Follow this thin stretch of river until it meets dry land. Jump off your Pokémon and collect the item on the ground.
This will be the Black Sludge.
Method 2: Stealing Black Sludges From Koga’s Muk
This method allows you to quickly collect as many Black Sludges as you’d like.
All you’ll need is:
- 8 Gym Badges and access to the Elite Four in Indigo Plateau
- A relatively strong Pokémon that knows Thief (you can get the TM 46 for Thief in Mahogany Town’s Team Rocket Hideout)
- A relatively strong Pokémon that knows Worry Seed (we’ll show you which Pokémon learn this below)
- A team capable of easily defeating Elite Four member Will – Dark, Ghost, and Bug-Type Pokémon are best for this
The idea is to use Thief to steal the Black Sludge that Elite Four member Koga’s Muk holds to recover its HP.
However, Koga’s Muk has the ability Sticky Hold, which prevents its held item from being stolen or destroyed. So you’ll need to disable Muk’s ability.
That’s where Worry Seed comes in.
Worry Seed replaces the opposing Pokémon’s ability with Insomnia, which prevents that Pokémon from falling asleep, leaving you free to steal their item.
You can most easily get Worry Seed in the following ways (note – the evolved forms of these Pokémon also learn Worry Seed, you’ll just have to wait a few extra levels).
|Level When It Learns Worry Seed
|Headbutting trees on Routes 26, 27, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 43, 47, and 48, as well as New Bark Town, Cherrygrove City, Violet City, Ecruteak City, the National Park, the Lake of Rage, and the Safari Zone Gate
|Route 48 (all day) and Routes 13, 14, 15, 32, and 33, as well as the tall grass in the Safari Zone Meadow Area (morning and day only)
|Route 24, the National Park, and the tall grass in the Safari Zone Meadow Area (day only)
Once you’ve got everything together, Fly to the Indigo Plateau.
Head inside, challenge the Elite Four, and easily destroy Will with your specially formulated anti-Psychic team.
Proceed to the next room and challenge Koga. Make sure your Thief user isn’t holding an item before you start the battle.
When Koga is about to send out his Muk, switch to your chosen Worry Seed user. Remember, it’ll need to be either fast or strong enough to successfully attack before it’s killed by a super effective Poison-Type attack.
After you’ve inflicted Insomnia on Muk, switch to your chosen Thief user.
Then all that remains is using Thief and receiving your prize.
Now you can either defeat the rest of the Elite Four for that sweet cash and EXP, or let Koga defeat you to quickly start the process again.
Tip: If you’d like to steal a Black Sludge by using Thief but don’t want to raise a Pokémon to learn Worry Seed, Biker Dale on Route 17 has a Gulpin that holds one too. However, you cannot repeat this battle, so you only have one chance.
Method 3: Wild Croagunk
Wild Croagunk, who appear in the Safari Zone’s Marshland Area after you place 42 forest blocks, also carry Black Sludge 5% of the time.
But since you’re in the Safari Zone, you’ll have to catch them instead of using Thief. So farming Koga is actually the better option.