From the time the game was released, it already published two special events. The first one was called Loyalty's Requiem where it featured a 16-man raid battle, and an event-limited 5-star Dragon. The one that followed it and currently running is called Trick or Treasure - which is the game's Halloween event. What this entails is that the game should most likely provide seasonal events to help pitch in some new content for players to continuously be interested in. For instance, this Trick or Treasure event, features a new story, a new boss battle, and a unique "Challenge" battle that takes you to survival kind of battle -- tasked to outlast the incoming waves of enemies.
Special events tends to reward players too with promotional units like special Wyrmprints, special season rendition of Characters (Halloween version), and this recent one even a brand new building to build in your Halidom. Special events also have a running period which most probably throw in some achievement tiers to render, and will reward you with unique items in return. For instance, the Trick or Treasure event will give you four special tokens that work like special currencies to enable you to redeem the different types of rewards listed below:
Candy Basket - Treasure Trade Rewards
Jack Chocolates - Treasure Trade Rewards
Snack-o'-Lanterns - Sweet Retreat Upgrades
Tricker Treats - Unlock Event Rewards