After you catch 200 pokémon in the Blueberry Pokédex, talk to Perrin to get some interesting information.

Talk to Perrin in the Terarium

When first you arrive in the Terarium, you will find Perrin near the entrance. Talk to her and she says to talk to her again after you catch 200 pokémon in the Blueberry Pokédex.

See the Photos

After you catch 200 pokémon in the Blueberry Pokédex, Perrin shows you two photos of rare pokémon in Area Zero. You can talk to Perrin again if you want to see the photos again. If you are playing Pokémon Scarlet, the photos will be of Gouging Fire and Raging Bolt. If you are playing Pokémon Violet, the photos will be of Iron Boulder and Iron Crown.

Gouging Fire

Gouging Fire is exclusive to Pokémon Scarlet. In Pokémon Scarlet, you can find Gouging Fire by going to Research Station No. 2 in Area Zero. Go outside, then turn right to see a waterfall. Go to the top of that waterfall, then look for the satellite dish nearby. Gouging Fire is standing near the satellite dish. It is level 75 and is a Fire/Dragon pokémon. One of the moves it knows is Burning Bulwark.

Raging Bolt

Raging Bolt is exclusive to Pokémon Scarlet. In Pokémon Scarlet, you can find Gouging Fire by going to Research Station No. 3 in Area Zero. Go outside, then turn right. Make your way along the grassy area toward the farthest tree that you can see, and keep going that way until you reach some water. Turn right to go toward the base of the waterfall. You will find Raging Bolt there. It is level 75 and is an Electric/Dragon pokémon. It knows the moves Rising Voltage, Thunderclap, and Dragon Pulse.

Iron Boulder

Iron Boulder is exclusive to Pokémon Violet. In Pokémon Violet, you can find Iron Boulder by going to Research Station No. 2 in Area Zero. Go outside, then go straight ahead. When you reach the edge, go straight down and you will land on a slanted piece of ground. Go down to the bottom of the slanted piece of ground. Go counterclockwise to go behind the slanted piece of ground, where you will find Iron Boulder. Check on it to start the battle. It is level 75 and is a Rock/Psychic pokémon. It knows the moves Mighty Cleave, Megahorn, Swords Dance, and Sacred Sword.

Iron Crown

Iron Crown is exclusive to Pokémon Violet. In Pokémon Violet, you can find Iron Crown by going to Research Station No. 1 in Area Zero. Go outside, then look straight ahead to see a waterfall in the distance. To the left of that waterfall, there is an archway below the top of the cliff. Climb up to that archway to find Iron Crown. Check on Iron Crown to start the battle. Iron Crown is level 75 and is a Steel/Psychic pokémon. Three of its moves are Future Sight, Sacred Sword, and Volt Switch.

Reward

After you catch the pokémon from Perrin's photos, put the pokémon into your party and talk to Perrin twice. After you have shown her both pokémon, you get a Sport Ball.