Interscroller
Interscroller ads are scroll-in ads, where creatives are fullscreen size, but visible through a viewport by scrolling through publisher content.
The viewport / placement size is the visible area purchased on the website where the ad will be published.
The size of the creative is set to 640 x 1280px that covers full screen on high aspect ratio mobile devices. When designing, bear in mind that most popular phones have a safe area of 854px.