Important Information

Please DO NOT reference this website as an official source when requesting permission on YouTube to prove you have obtained the rights to monetize your videos. This is just a summary of the information I was able to find through my own research. I have provided sources for each company I researched so you should either use those resources or reach out to the company yourself if you need it. Please do not contact me with help trying to monetize your videos on YouTube!

Things you should be aware of

You should also be aware of a few other things before concluding that you might be safe to monetize your videos:

Developers / Publishers

Games may have several entities credited such as developers (who make the games) and publishers (who help finance and publish the games).
In many cases, especially for indie developers, the developer may own the rights to the game unless it uses licensed content (which we'll get to). However, publishers may also retain rights to the IP, especially if the development studio is a subsidiary to the publisher.
Publishers, game holding companies, etc, may own several other publishers or development studios as subsidiaries, such as Sony Interactive Entertainment.
In some cases, multiple developers may work on a game, such as Certain Affinity, which has worked on multiplayer gameplay for several games with other developers under different publishers, such as Halo and Call of Duty games (though, in this scenario, Certain Affinity would not have any say in your YouTube content).
Sometimes games are published by multiple publishers
- In the example of Mario & Sonic at the Olympic Games, the game was developed by Sega Sports R&D (a subsidiary of Sega), and published by Nintendo in Japan, but Sega worldwide. The game also features characters and IP owned by both Sega and Nintendo.
- It is also possible for a game to have different publishers for different platforms.

Ownership can be transferred

Much like film & TV, video game rights, as well as the developers or publishers themselves, are often transferred, sold, or acquired by different entities very frequently.
- An example is Sunset Overdrive, which was owned by developer Insomniac Games, and published by Microsoft. Insomniac Games has since been acquired by SIE and now Sony owns the rights to Sunset Overdrive.
- As is the industry, there are often studio closures that lead to selling off assets, such as Telltale Games, which sold off its assets and licenses and had most of them obtained by LCG Entertainment Inc. (which also secured and is now using "Telltale Games" for its releases).
  - Sometimes games from defunct studios are not purchased. This means that while there are no rights holders to worry about for your videos getting claimed, there would also be no person to contact when it comes to obtaining permission to monetize your videos should YouTube insist on proof or in case of false claims.

Licensed IP and music

Many publishers and developers create games based on licensed properties. This could be franchises (such as Star Wars), characters (such as Marvel characters), toys (such as LEGO and Transformers), board games (such as Hasbro), cars (such as Mercedes-Benz), instruments (such as Fender or Gibson), or even a person's likeness (such as Travis Scott in Fortnite). Use of any of these falls outside of the game publisher or developer and would even more difficult to obtain permission, especially from bigger companies like Disney in regards to monetization.
Many games feature licensed music that will likely result in copyright claims on your videos. Only the music rights holder would be able to assist with this issue. It is best practice to remove the audio or music volume from your videos in order to prevent any possible claims on your videos.

Policy may vary by game