It's apparently being created as a result of an app that you have installed that contains ads. Several different culprits are identified in this thread:
http://forums.androidcentral.com/samsung-galaxy-note-2/274155-applifier-video-cache.html (most notably the Hill Climber Racing game).
Is that folder created in your "SD card"? If so, you might try this:
- turn off wi-fi and 3G/4G temporarily (so that the offending app cannot communicate with the outside world)
- remove the "unityadsvideocache" folder again
- manually create the "unityadsvideocache" folder with a file browser (i.e., using the same one that you removed it with I would imagine)
- turn wi-fi and 3G/4G back on
My rationale for the above is that ownership/permission of the file browser creating that folder first before the spamming advertisement might keep the spamming ad s/w from adding those video files to that folder because it wasn't the one that created it.
This might not work depending on your version of Android but then again...it might
and is an easy thing to try/do.
BTW, the suggestion in that AC thread to create a .nomedia file won't help--that will just hide those files from being presented by some apps.