Well, there is a method accessible to anyone actually! But only for new Tibia accounts! You will get this free mount in 3 different characters under the following conditions described in the "Tell-A-Friend" section of Tibia official website:
Rewards of Your Friends
Players that create an account after having received an invitation from a Tibia player will be rewarded with a "Rented Horse" which can be used on the first 3 characters on the account within the first 7 days after account creation.
Keep in mind that you can use this mount anywhere for the limited period of time mentioned. So if your char goes to Dawnport, Mainland, Island of Destiny, Rookgaard, etc, his mount will stay with him. Interesting ideas for screenshots I guess
My referral link is the following one if you want to help me: https://www.tibia.com/mmorpg/free-multiplayer-online-role-playing-game.php?taftoken=ce85f874-a94f-4a65-9116-1aa9a0fc839c
But you can send your personal link to another email and get a new account with this small bonus in Tibia. In order to do that, access the "Tell-A-Friend" section once accessing your Tibia account at the Tibia official website and click in the option where you can send the link by email.