[delroth]

Most game studios these days - including Nintendo - explicitly provide guidance and licensing terms for content creators. You can for example check out https://www.nintendo.co.jp/networkservice_guideline/en/index...

> As long as you follow some basic rules, we will not object to your use of gameplay footage and/or screenshots captured from games for which Nintendo owns the copyright ("Nintendo Game Content") in the content you create for appropriate video and image sharing sites. To help guide you, we prepared the following guidelines: [...]

The legal gray area definitely still exists for many of the smaller/indie game studios, but this kind of licensing is more common than not today.