The simple answer is that it's legal but if Hasbro decide to sue you it won't matter because you won't have the cash to argue and anyway they'll lean on your hosting service who will cut you off in a moment.
This is exactly the state things got to in the dying days of TSR (when they became known as They Sue Regularly); they never got anywhere near a court but it didn't matter. Of course, they lost a ton of free publicity and goodwill which helped to sink the company, but that's the legal world for you.
d7 has an archive of the sorry mess that was the TSR legal fiasco so you can go and watch a company commit suicide if you like. Stand out quote: '"They don't have to. All they have to do is threaten legal action and the administrators will back down. I mean... who really cares about a bunch of gamers?"'
TSR didn't, for one.
It is amazing what people think is covered by copyright despite all the relevant law being available online. Characters is a classic; they're not. This has been tested in US and UK courts many times. They may be covered by trademark, but that only really matters when you're, well, using the name to trade with. Having James Bond in a book is not (and has never been) a problem if you keep his name of the cover and the publicity material. The same applies to words like "Greyhawk", let alone stuff like "Orcus" or "Fireball".
There is the possibility of odd exceptions, though. In the UK it is dangerous to do anything with Peter Pan as the work is specifically and individually legislated for in this country, so a "Peter Pan" module might actually attract some trouble even though copyright has technically expired, if you quote chunks of text. But, again, all the written law is online so you can check yourself and decide.
Remember: every court case has two lawyers who generally have opposing opinions based on the same laws; don't blindly trust them any more than you blindly trust anyone else you'll be paying by the hour.
Also note that copyright and trademark law has moved on since the 1990s, so don't take the arguments in d7's archive as gospel. The idea of trademark "domains" has been greatly blurred in the US and other countries since then, for example.