The day after you meet Professor Tangrowth, Squirtle, Bulbasaur, and Charmander, the professor wants to investigate a nearby building.
Talk to the Professor
Go to where the professor went (look for the speech bubble in the distance). In this area, there will be glowing spots on the ground, red Pokéballs, and sparkling objects. However, if you try to go too far away from the professor, they will call you back, so when you're ready, talk to the professor.
Check on the PC
Check on the PC to continue. Then open the Challenges menu. You can earn Poké Life coins by completing these challenges.
Complete a Challenge
Before you continue, you should complete one of the challenges: find a new Pokémon by creating a new habitat, water trees, or gather sturdy sticks.
Use the Shop
Check on the PC and go to the Challenges menu, and choose the completed challenge to receive Life Coins. Then open the Shop to get an explanation of how to use it.
Complete the Remaining Challenges
Next, you have to complete the other challenges that you haven't done yet.
Explore the Area
Check on the Pokéballs to get items, check on the sparkling objects to get Human Records, which you can review in the Collection menu in the Pokédex, and and check on the glowing spots to add habitat hints to your Pokédex. This will tell you which habitats you can build for a chance to make new Pokémon appear.
Help Bulbasaur
After you complete the first three challenges, talk to Bulbasaur. They give you leaves, then ask you for a relaxation item. You'll learn a recipe for a Straw Bed, so go to the workbench and create a Straw Bed. Go to Bulbasaur's habitat (a set of four tall grasses) and press the right control stick like a button to see an outline of Bulbasaur's habitat. Put the straw bed anywhere inside this outline. Then talk to Bulbasaur to complete their request.
Build Your House
Use the PC to buy a Leaf Den Kit. Place the kit where you want to build the leaf den, then check on it to see what materials are required. You will need to find a boulder and water the grass around it, then use Leafage to grow four sets of tall grass to create an environment where Timburr can appear. When the grass around the boulder starts shaking, check on it to meet Timburr. Check on the leaf den and press R to see which Pokémon to bring. Then talk to those Pokémon and ask them to follow you, then go back to the leaf den and make sure the Pokémon are nearby, check on the leaf den and press R to see the list of Pokémon, then you can press + to request their help. Do the same on the other tab to add the required materials, then choose Start Building to start building the den.
After the den is finished, talk to Timburr to reveal the new house, then talk to Timburr again. Get three different pieces of furniture, then go into the leaf den and put the three pieces of furniture into the den. (Since Ditto likes a bright environment, consider putting a campfire or other source of light in the den. Have Charmander follow you into the den to light the campfire.) After you have placed three pieces of furniture, go outside and talk to Timburr. Then talk to Charmander, then talk to Professor Tangrowth.
Put the Ditto Flag on your House
Stand next to the leaf den you built and press X to open your bag, then choose the Ditto flag. Put it on top of your house to continue. You will learn the recipe for the Ditto Flag.
Afterward, talk to Professor Tangrowth.
Unlock Moves
You can now learn new moves by exploring the Withered Wastelands. Read the List of Ditto's Moves to learn how to unlock these new moves.
Raise the Environment Level to 3
If the Environment Level is lower than 3, read How to Increase the Environment Level and take steps to improve the environment level until it reaches 3.
Buy a Pokémon Center Rebuilding Kit
The Pokémon Center Rebuilding Kit costs 1000 Life Coins, so if you don't have enough, complete challenges until you have enough.
Explore the Cave
Use Rock Smash to break the rocks west of the Pokémon Center, then go with Squirtle to explore the area. When Squirtle departs, explore the cave until you hear a Pokémon calling out to you. Break the rocks in that area to find Onix. Talk to Onix and try to break the rocks in Onix's way. Then talk to Professor Tangrowth. They won't be at the Pokémon Center, so go south to find them. Talk to them and explore the southern area together. Follow them to the building and check on the box in front of the building. Afterward, go back to the Pokémon Center and talk to Professor Tangrowth.
Make a Seaside Tall Grass Habitat
Go back to the beach and create a Seaside Tall Grass habitat, then wait for the grass to start shaking and check on it to meet Slowpoke. Talk to Slowpoke, then create some wooden steps and make a path to the Pokémon Center for Slowpoke. Be sure to water the path to make it easier to walk on as well. Then talk to Slowpoke and wait for them to reach the Pokémon Center. When Slowpoke says "I made it", talk to them to continue.
Raise the Humidity
Use Water Gun to water the grass nearby. Then when Professor Tangrowth says "Looks like you sprayed some water" talk to them. Then talk to Slowpoke and ask them to Yawn. Afterward, talk to Slowpoke when they mention spring water. If you can find more dripping rocks in cliff walls, be sure to use Rock Smash to break them. Is one north of the Pokémon Center that you can break to fill some ponds, including one that contains a fountain. After you reactivate the fountain, talk to Slowpoke.
Talk to Other Pokémon
Talk to Squirtle
Talk to Squirtle and create a Hydrated Tall Grass Habitat (break the dripping rock in the cliff wall to fill the pond, then use Leafage to create grass around the pond). Then talk to Squirtle and have them follow you, then go to the Hydrated Tall Grass Habitat and talk to Squirtle and ask if they want to move there.
Talk to Bulbasaur
Talk to Bulbasaur and create a Field of Flowers Habitat (you can buy Wildflower Seeds from the Shop in the PC and have Bulbasaur follow you to make them instantly become full-grown; see List of Ditto's Moves to find out how to learn Rototiller so you can create dirt to plant the seeds in).
Talk to Squirtle Again
Talk to Squirtle to learn about a Rain Dance party. Then talk to Professor Tangrowth, then go up the stairs south of the Pokémon Center to reach the cave where you met Professor Tangrowth. Check on the wheelbarrow to find the Castform Weather Charms. After you place a Castform Weather Charm, you can check on it to flip it over, but since you want the rainy side up, you can leave these as they are for now. Use them to create a Rain Dance Site. The dolls need to be placed on a wall. You can buy a Wooden Plate from the Shop in the PC, or if you learned the recipe for a Wooden Plate, you can make one at a workbench. After you create the habitat, talk to Squirtle, have them follow you, then face the Rain Dance habitat. Wait for Squirtle to finish the rain dance, then talk to Slowpoke and ask for a yawn.
Go to the Ocean
Follow the other Pokémon to the ocean. Use Cut on the fallen logs (see List of Ditto's Moves if you don't yet know Cut), then use a Workbench to make Bridge Planks, and build a bridge so you can reach the big Pokémon in the water. Four sets of Bridge Planks are enough. Talk to the big Pokémon to continue.
Rescue Onix
Go back to the cave where Onix was trapped. The rain has softened the blocks in front of Onix, so use Rock Smash on them to get rid of them. You will learn a recipe if you pick up the Squishy Clay that the blocks turn into when you break them.
Talk to Professor Tangrowth Again
After Onix says they can get out, talk to Professor Tangrowth. This completes the request "Yawn Up a Storm".
Make a Home for Onix
Go back to the cave and talk to Onix to learn about the Smooth Tall Grass habitat. You can find a Smooth Rock in the cave. There are some rocks you can break with Rock Smash to open new paths in the cave. You can also use Leafage on dry soil to create dry tall grass, then use Rototiller to put the dry tall grass in your bag so you can put it down and make a habitat for Onix. (See List of Ditto's Moves if you don't yet know Rototiller). Make sure that you create this habitat in an area that doesn't have any openings in the ceiling where rain can come through.
Finish Rebuilding the Pokémon Center
Now that you have rescued Onix, you can rebuild the Withered Wasteland Pokémon Center.
If you don't have enough materials, you can cut down piles of logs or trees to get Small Logs, which you can take to Scyther to turn into Lumber. You can use Cut on vines hanging from cliffs, or pull up leaves from the ground, to get leaves and Vine Ropes.
Then look at the list of Pokémon who can help rebuild the Pokémon Center and have them follow you, then request their help when they are near the Pokémon Center. Then when everybody is gathered, start building.