If I were to buy a domain and create a website out of it using a name of a company, would it be considered illegal? For example, if I added "NintendoWii" in a domain, what would happen?
If it were a fan forum you may or may not get a Cease & Desist. If it's to speak ill of the company... then expect legal backlash.
You are using a trademarked name and infringing on it. What's done or not done is up to the company. They may allow it, but they also could snatch it up at any time if they really wanted to.