Time: 2010 (PDT 18:00, June 21st - 18:00, July 5th)
NPCs：
| Name | Location | Services |
| Fiend Lair Herald | Market (303,250) | 1. Introduces the quest. 2. The teleporter to the Fiend's Lair. |
| Crystal Merchant | Market (303,254) | 1. Sells Lair Permit. 2. swaps your crystals for CPs. |
| Fiend Lair Guard | Fiend Lair F1-15 (194,166) | 1. Gives the quest. 2. Opens the portals to the next floor. 3. The teleporter to the market. |
Admission:
1.F1-F10: Pay 10,000 Silver to Fiend Lair Herald Market (303,250). He will send you to the first floor, and you can start your journey to floor 2-10 by completing the Fiend Lair Guard's quest.
2. F11-15: Purchase a Fiend Lair Permit from Crystal Merchant (Market 303,254). Right click the permit to enter the corresponding floor.
| Fiend Lair Permit | Cost |
| F11 | 10 CPs |
| F12 | 50 CPs |
| F13 | 100 CPs |
| F14 | 200 CPs |
| F15 | 500 CPs |
Rewards:
| Fiend's Lair | Boss Drops |
| F1 | No drops |
| F2 | 5,000 silvers |
| F3 | 10,000 silvers |
| F4 | 15,000 silvers |
| F5 | 25,000 silvers |
| F6 | 50,000 silvers |
| F7 | 100,000 silvers |
| F8 | 150,000 silvers |
| F9 | 200,000 silvers |
| F10 | 250,000 silvers |
| F11 | 1/6 exp ball or 5 / 10 / 20 / 270 / 1,380 CPs |
| F12 | 5/6 exp ball or 25 / 50 / 100 / 1,350 / 6,900CPs |
| F13 | 1 and 2/3 exp ball or 50 / 100 / 200 / 2,700 / 13,800 CPs |
| F14 | 2 and 1/2 exp ball or 100 / 200 / 400 / 5,400 / 27,600 CPs |
| F15 | 3 and 1/3 exp ball or 250 / 500 / 1,000 / 13,500 / 69,000 CPs |
Walkthrough：
1. Find and speak with the Fiend Lair Herald in the Market (303,250), and you will hear the details of this treacherous place. You can pay 10,000 Silver to enter the first floor, and start your journey down into the depths.
2. You can choose to kill the bosses on the current floor, or move on to the next floor. Talk to the Fiend's Lair Guard (194,166), if you want to go on to the next floor. They will give you some tasks to complete, before they will be able to open the Fiend's Lair Portals for you. Once you kill the boss on the current floor, you will be teleported back to the Market.
3. After you complete the task, the Fiend's Lair Guard will open the portals for you. The portals are old magic, and the instability causes them to not work perfectly. They will randomly send you to the next floor, back to the last floor, or keep you on the current floor. There are 4 portals on each floor, and you must select the correct one, if you hope to continue on.
4. If you want to enter the 11th~15th floor, you'll need to find the Crystal Merchant (Market, 303, 254) and purchase one of his Fiend's Lair Permits. You will be directly teleported to the appropriate floor, rather than having to walk there. A permit can be used only once.
5. Kill the bosses on Floor 11-15, and you will have chance to obtain EXP and even Crystals! Right click the crystal to obtain huge EXP directly, or sell it to the Crystal Merchant for CPs.
