How do you find a pink gooey thingy on Pokemon diamond?

You're likely thinking of Pinkan, a rare Pokémon that appears as a pink, gooey blob. However, Pinkan is not actually in Pokémon Diamond. It was introduced in Pokémon Black and White.

Here's what you can find that might be similar in Pokémon Diamond:

* Squirtle: While not gooey, Squirtle is a water-type Pokémon that can learn moves like Bubble, which creates a pink, bubbly effect. You can find Squirtle in Lake Verity.

* Spinda: This Pokémon has a unique pink and white pattern, resembling a gooey blob. You can find Spinda in various locations, including the Grand Underground.

If you are playing Pokémon Diamond, you won't find Pinkan. It's important to remember that each generation of Pokémon games introduces new creatures, and some older Pokémon are not available in newer titles.