How do you catch virizon?

It seems you might be asking about Viridian, not Virizon. Viridian is a term used in various contexts, like:

* Viridian green: A shade of green.

* Viridian City: A city in the Pokemon games.

* Viridian Forest: A forest in the Pokemon games.

If you're asking about catching a Pokemon in Viridian Forest, you'd need to use Poke Balls after weakening the Pokemon with attacks. Please tell me more about what you're looking for so I can give you a more accurate answer.