Wouldn't making a game guide be fair-use, similar to an unauthorized encyclopedia of a fictional universe (like Middle-Earth)?
Even so, I suppose you'd have to defend the fair-use in court.
Even so, I suppose you'd have to defend the fair-use in court.
If they've published their own game guide, just don't take any material from it and you won't be violating any copyrights on that either.
For trademark, the point is to prevent consumers from being confused about who is responsible for products, so people can build up a brand name and have a reputation they are responsible for and have control over. Guide titles like, "Ubergeek's Ultimate Unofficial Guide to Diablo 3" do not violate trademark because they do not cause any confusion about whose product this is. It's well established that you can use someone else's trademark as a substring in your product title when it's important to explaining what your product is and won't cause consumer confusion. (Similarly, "Pegasus Case for iPhone" or "Ubergeek's iPod Battery Replacement Kit" would not violate trademark.)
But, yes, as you say: being completely right doesn't prevent you having to defend yourself and spending time and money on that. (Could you recoup lawyers fees after you win? I have no idea about that.)
DISCLAIMER: I am not a lawyer. (But I have read some legal sources about this.)