Hi Samantha:
We use a Reachforce on our Marketo landing pages.
You can create a Marketo form and then have the other Reachforce-enriched fields hidden and populated by the Reachforce data on submission. The JavaScript that Reachforce provides can just be copied and pasted into your landing page template head after the corresponding hidden fields with no default value are set up on the form.
Making a custom form on a Marketo page with HTML would be a burden to implement and maintain!
Best,
Edward UnthankMarketing Operations Specialist
Yesler