As announced on September 20th, 2022 in the article: Welcome to Splinterlands Tower Defense, Splinterlands Tower Defense (SPLTD) takes a page from the Splinterlands playbook as an auto-battler. You will make strategic choices, such as the placement, upgrading, and arrangement of your towers, spells, and heroes during the preparation phase. You will then commit your defensive strategy to the battle. You can then either watch the battle play out at various speeds or skip to the results.
Packs can be bought on the Tower Defense tab of the Shop page within Splinterlands.
To find them go to the Other tab of your inventory (=cards page) Or watch the video, for a more detailed explanation.
More information on the presale can be found here: Presale FAQ – Splinterlands