Each Tiers offers two tracks for Milestones Rewards.
The first track is accessible to everyone.
The second track (premium track) can be unlocked by purchasing the relevant Premium Pass.
For both tracks, rewards can be collected when sufficient progress has been made.
The premium rewards track includes currencies such as Gems and Stones, and a premium Tower skin.
When purchased via the Web Store, a Premium Pass also grants a certain amount of Gems instantly.