Onix is one of the rideable Pokemon in Let’s Go Pikachu, Eevee, it is also one of the biggest Pokemon you can ever find in the game. You can catch one of this Pokemon in the Rock Tunnel, from Route 10.
You can reach this area after learning the Secret Technique Light Up from the assistant of Dr. Oak.
Your rival partner, actually lead you to the way going to the Route 10, where the Rock Tunnel is. East of Cerulean City.
Before reaching the entrance of the Rock Tunnel in Route 10, you’ll be encountering here some Team Rockets and the Elite 4 Pokemon League, miss Lorelei. From here, the entrance to the cave is just on the left corner.
Outside the entrance of the Rock Tunnel, there’s a Coach Trainer Tasha which you can also fight to get a TM13 Brick Break.
Once you’re in the cave, you’ll be using the Secret Technique Light Up to visibly see the area.
This is where the Onix spawned.
How to Successfully Catch Onix
You need to bring at least 3 to 10 Great Poke Ball.
Go to the Rock Tunnel and hunt for the Onix, the spawning area is near the entrance. Onix spawn in the Rock Tunnel every 1 to 3 minutes. If you ride Persian, it can sniff something in the ground and the Onix must be spawn much quicker.
No need to tame for foods, just use your Great Poke Ball. In our case, we only use 2 Great Poke Ball and we’re able to catch Onix.
You probably catch the Onix and you can use it for Pokemon back riding.
You may also watch our walk-through video guide below.
You can also catch one as early as Mt.Moon, although it is rare. However, I only encountered one, caught that one, and did not need a lure. Best of luck to others.