Raid Boss
Play the Raid Boss event with your Guild to prevent Zuul'Goth the Elder God from escaping the Portals into the world of Krystara. Raid Boss occurs once every 3 weeks and is a co-op Guild event. Do as much damage as you can to the Raid Boss with your Guild to close Portals and earn Rewards.
Overview
You can find the Raid Boss event by opening the Guild menu on the World Map and selecting Raid Boss.
On the Raid Boss Overview screen, you can see:
The current Raid Boss
Your Guild's progress
The damage you've done so far
How many Sigils you have
The Kingdom the Raid Boss is trying to enter.

The aim of the event is to band together Troops from the Kingdom the Raid Boss is trying to enter: Therefore your Troop filter is locked to using Troops from the Kingdom in danger.
Every battle in the Raid Boss event costs 1 Sigil to play. Every player will receive 4 Sigils at the start of each day (07:00AM GMT), you can gain more by defeating Valravens or purchasing them in the Raid Boss Shop.
Fight Minions and Mini-Bosses
Before you can fight Zuul'Goth, first you must defeat his Minions and the 2 Mini Bosses in the first 4 stages of the event. These stages are played individually; you cannot help your Guild battle Zuul'Goth or collect Portal Rewards until after you have completed the first 4 minion stages. Once completed, you can collect rewards for defeating the Minions on the Rewards tab.

Battle Zuul'Goth and close the portals
Once you have defeated the Minions, you can now battle Zuul'Goth. The aim is to do as much damage as you can to him before the event ends in order to close as many Portals as possible. Each time you defeat Zuul'Goth by winning a battle, he gains 5 Levels.
As you do damage to Zuul'Goth you will close Portals, which can be seen on the Rewards tab - where your damage counts as points or a score. There are 20 Portals to close, and your Guild must work together to close as many as possible. For every Portal you close, your whole Guild can collect rewards from the Rewards tab. If you have uncollected rewards when the Raid Boss event ends, they will be sent to your in-game mail.

God Slayer Event Troops
A new God Slayer will be released at the start of every Raid Boss event. God Slayers have special spells and traits which allow them to do a LOT of damage to Raid Bosses. You can purchase God Slayers in the Raid Boss Shop using Gems.

Menu Overview
Raid Boss Shop
In the Raid Boss Shop, you can use Gems to purchase special Raid Boss packs which will help in your battle against Zuul'Goth. Items they can contain include:
Souls to level up your new Troops
Gold
Sigils
Event Troops
God Slayers
Special Weapons from the event Kingdom
Traitstones to upgrade your God Slayer
Diamonds
Ingots to Level-up your Weapons
Each Shop Tier must be purchased in order; however, Stage VII (6) of the Raid Boss shop can be purchased as many times as you want.

Guild Tab
The Guild tab shows how every member of your Guild is doing in the event. The Guild Roster here is sorted by the highest Boss level and damage dealt to the Boss.

Leaderboard
The Leaderboard shows the 100 players globally for your Platform who have the highest Raid Boss level and who have done the most damage during the current Raid Boss event. The players in the Top 100 will earn extra rewards when the event is over. You can also see how you compare with the rest of the community here.

Tips
Sigils will accumulate day to day during the event. You will earn 4 each day; however, they will not carry over into the next event, so ensure you use them before the Weekly Reset
If you want to spend the least Gems possible, try purchasing at least Tier III so you can get the maximum damage possible with the Event Weapon and the God Slayer Troop
Try to defeat the Raid Boss as soon as possible and worry about the other 3 Troops once the Raid Boss is defeated
Consider using Weapons which remove all armour to defeat the Raid Boss more quickly, such as Mang or Fleshripper
Remember Zuul'Goth is immune to all status effects, so go for high damage-dealing Troops over ones which cast status effects.