The legendary Pokémon Terradon can be found in the Earth Temple, deeply hidden in the forest. However, in order to capture Terradon, the player must first destroy the plans from Team Solar and Team Lunar. You will also need the Earth Core and have a Ground-type Pokémon in your Party.
Dullfern Forest is a big forest that's somewhat maze-like. It is filled with spider webs that can be cut down with Clippers. Each spider web contains a wild Spidox that will attack you. However, they will only attack if you interact with the webs then use the Clippers; using the Clippers if they're registered with F5 will not work, but will allow you to pass without a battle. The first temple of the region, the Earth Temple, is located deep in the forest. Upon your first visit, you can see two Lunar Grunts with Team Lunar Officer Scarlett, talking about their plans in front of the temple. When they spot you, you have to battle them in order to make them leave and continue on with the main story.
When you initially enter the forest, Rick is standing next to the first spider web. He will challenge you only after you've cut down the web. If you haven't obtained the Clippers yet, you must defeat Gym Leader Donna and defeat all 4 Trainers in the Trainer's School, then you will receive them from Bella. Be careful, YOU MUST INTERACT WITH THE SPIDER WEB, THEN USE THE CLIPPERS; USING THE CLIPPERS WHEN REGISTERED WITH F5 SOFT-LOCKS THE GAME, FORCING A SOFT RESET WITH F12. His team is as follows: