From the in-game help:
Once a month every Guild will be given a set of quests to complete.
Quests range from easy to hard and rewards improve depending on the difficulty.
- Quests must be completed by the end of the week [the event runs over the weekend for 4 full days]
- Every member will be rewarded for completed quests
- Members may only assist one quest at a time [this doesn't appear to be true - guild members can work on two quests at a time]
Easy Quests[]
- Help 600 Times - Help Adventures and Challenges to assist
- Send 500 Gifts
- Bounty 50 Vikings
- Battle Bosses 100,000 Times - Battle bosses to assist
- Win 3,000 Battles - Win Chieftain battles to assist
- Complete 1,000 Adventures - Do Adventures you haven't earned achievements for yet
- Complete 15 Challenges - Complete challenges to assist
Medium Quests[]
- Battle Bosses 300,000 Times - Battle bosses to assist
- Win 7,000 Battles - Win Chieftain battles to assist
- Complete 2,500 Adventures - Do Adventures you haven't earned achievements for yet
- Complete 40 Challenges - Complete challenges to assist
Hard Quests[]
- Battle Bosses 600,000 Times - Battle bosses to assist
- Win 15,000 Battles - Win Chieftain battles to assist
- Complete 5,000 Adventures - Do Adventures you haven't earned achievements for yet
- Complete 60 Challenges - Complete challenges to assist
Rewards[]
Easy[]
One each of (2 in total):
- 5% Energy boost or Gold boost
- Basic Warrior / Weapon drop
Medium[]
One each of (4 in total):
- up to 15 FP (in denominations of 5)
- 5% Energy boost
- Gold boost
- Better Warrior / Weapon drop
Hard[]
A combination of (5 in total):
- up to 100 FP (in denominations of 5)
- 5% Energy boost
- Gold boost
- Looter Warrior / Weapon drop
- Better Warrior / Weapon drop