You can create promotional tickets using the “hidden ticket” option. Create a promotionally-priced or discounted ticket and check the “Hide Ticket” box so it will not be visible to the public on your event page.
You can create as many hidden promotional tickets as you like and then share them via email or other method directly with your end user.
Publicly, your event page visitors will only see regular tickets (those that do not have “Hide Ticket” box checked). And only the people you share the promotional tickets with will be able to purchase the discounted ticket.