I made a HTML5 banner of my website. I want to host it on my server and provide it to other sites with an Iframe. Is this bad for SEO?
Will the link on the banner as a link pointing to my site? In such case what can I do so it counts towards Google rankins/how else can I include the banner outside my site?
It won't affect your SEO since iframe aren't search engine friendly. A better way to do this is to use JavaScript to provide the banner and then use
<noscript>
to link back to your website. Then you will benefit from SEO as that link is a positive ranking factor in all search engine algorithms.