Which IAB Rising Star ad is anchored to the bottom and can be initiated by click or rollover?

The Slider ad is designed to be anchored to the bottom of a webpage, typically sliding up into the viewable area when activated by a user interaction such as a click or a rollover. This specific functionality makes it particularly engaging, as it provides a dynamic user experience without completely taking over the page upon initial loading. The reason it is often selected in advertising campaigns is that it allows advertisers to capture users' attention in a non-intrusive way while still encouraging interaction.

In contrast, other ad formats mentioned, like the Portrait and Billboard, have different placements and interactivity styles. The Portrait typically appears on the side and does not slide into view in the same interactive manner, while the Billboard is a large format that generally covers the top part of the page without a roll-in feature. The Pushdown ad also expands from a standard banner but is not configured to slide smoothly into view like the Slider. Hence, the unique characteristics of the Slider make it the correct answer in this context.