Advertisers using video ads on YouTube can now expand their reach as in-stream ads and bumpers have been introduced on YouTube Playables within the mobile app.
This update, spotted on Google’s help page, allows skippable, non-skippable, and bumper ads to run automatically before and during casual games, without requiring any additional setup from advertisers.

Read the official help page: About video ad formats.
This update was spotted by Hana Kobzová.