The event pass has two rows: regular and premium. Points unlock both rows at the same pace, but the premium row is only available to those who pay for it for that event.
The regular row is free and generally contains energy, coins, XP, roots and herbs, food, region-appropriate materials and gems. Rewards can be doubled by watching an ad.
The premium row is only available when bought and contains a costume, more energy and food, green rings, good equipment and gems. Once the end of the premium row is reached, additional points unlock gift boxes which have a random chance of giving energy, gems, food, xp or a green ring. Additionally, buying the premium row will activate a special speed potion for the remainder of the event. If you already have a speed potion active, its time will be added, not lost. If you have the premium row active all rewards from the regular row are doubled automatically, without watching ads.
The event pass ends when the event ends (not a week later). You can claim the rewards while the event is active. If you forget to claim rewards, they will all be added automatically when the event ends (including the extra points-boxes for the premium row).
Re-released events do not have the event pass, so most costumes from past premium rows are currently impossible to get if you didn't buy it when the event was first released. However, one is available in the shop for gems, so more may appear later.
For a list of event pass items in a specific event, see Events.
All released costumes can be seen HERE