Hands-on marketer, an extension of your team.
Email list building - Focus on making your sales funnel perform, and perfecting your email list building path via lead magnets.
https://www.listbuildify.com/
Customer discovery - Use of a mix of principles from customer discovery (get out of the building), lean startups (iterative loop of experimentation), startup engineering (disprove your assumptions), and the business model canvas to uncover your compelling business model, by doing “un-scalable” things to reach out to "ideal" users.
https://www.tractionmate.com/