YouTube has now disabled the creation of Annotations, and instead has given us End Screens and Cards, but I can't see how to recreate this particular look with either.Is this an advertisement? If so, what type? It doesn't seem to appear in their advertising documentation, either (which states that overlay advertisements are 480x70).
What is this advertisement on the bottom-left of a YouTube video?
video;youtube
This is a call to action overlay (which is different from an overlay ad). CTA overlays are available in advertisements (if a video ever has been used as a video ad, any CTA overlays that have been inserted during the campaing remain on it afterwards), for non-profit accounts and for twitch live notifications. 