What object in Campaign Manager is equivalent to a creative in Display & Video 360?
If you use Display & Video 360 with Campaign Manager, Display & Video 360 creatives will be served by Campaign Manager as part of a placement.
In Campaign Manager, a placement may contain multiple ads, and each ad in the placement may be associated with multiple creatives (all hosted in Campaign Manager). Thus, it’s common for a placement to be associated with multiple creatives.
Read more here: https://support.google.com/displayvideo/answer/3217641