Hi,

Say I'm developing a walkthrough for popular game "Infinity Blade" on the appstore. Am I allowed to name my app: "Infinity Blade Walkthrough" or "Walkthrough for Infinity Blade III" and specify in the description that there's no affiliation between it and the trademarked name ?

What's legal and what's not here ?

On 6/10/2018 at 2:35 AM, Deliverance said:

What's legal and what's not here ?

There is a lot of detail involved, and it is location specific.  You should talk with a lawyer in your region who is familiar with both video games and IP law.

In general terms you are allowed minimal nominative use.  That is, you can generally use the name of a thing to call it by its name.

It gets more complicated the more you use the names, and based heavily on how they are used. It also gets more complicated if you are using images or sounds, and how they are used.  You can generally use some of those, but generally only the minimal amount needed to communicate your information. You also generally cannot use them in a way that implies any kind of endorsement or acceptance or relationship, either positive or negative.

And there is also the risk of lawsuit versus actual legality, the two are not completely aligned. Many people cross the line but are never contacted by the legal team, some people don't cross the line and face legal action. 

On 6/10/2018 at 2:35 AM, Deliverance said:

Say I'm developing a walkthrough for popular game "Infinity Blade" on the appstore.

In that case you're probably fine as long as you are clear that you are not affiliated with the companies or the game in any way, you never disparage or write negatively about them, and you keep it specific to the walkthrough steps as a guide.