Q: What is Devil's Square?
A: Devil's Square is an event more than a map. It takes place roughly every hour and the NPC is located in Noria. To enter Devil's Square you must first make an invitation. To get an invitation you need a Sneak Eye and Devil's Key. You then combine them in the Chaos Machine - a key will pop out and you can then enter Devil's Square. You wait until the timer on the key reaches 0 and you speak to the NPC in Noria. You can then choose the difficulty, depending on your level. On the hardest difficulty, the mobs go all the way to Vimknights. If you are able to solo a Vimknight then chances are you will still die, since when I mean Vimknights I mean Vimknights EVERYWHERE. ie, you can't move for the buggers, and they're all pounding at you.
Q: What is Blood Castle?
The Blood Castle is the hardest map made in MU to date. It consists of you battling your way into a castle, being hit on all sides by the strongest mobs in the game. The 2nd weakest mob yeilds a Chaos Dragon Axe, so that gives you an idea of the compition. The main battle is actually just reaching the enterance to the castle, as you cannot just walk up to it.
You have 15 minutes to reach and break through the door, and you must accumulate a certain amount of kills before you can attack and break down the door. Getting to the door in the first place requires power, concentration, and precise clicking. The mobs constantly regenarate and you are battling through a narrow ledge completely jam-packed with them. BKs with 700 defense will be completely mauled; let me tell you. (The door has like 50k HP too btw).
When you're through the door the real battle begins, as the whole event is actually a race against the other players. Past the door you will fight the hardest mobs in the game, but Blood Castle-exclusive mobs; you don't seem them anywhere else. These mobs drop Phoenix Feathers - the item required to make 2nd class wings, but they drop very rarely, and if you're going for the cup you'll have other things on your mind.
You must walk straight into all these mobs and start beating the living crap out of a huge coffin-like object. It has several layers, each stronger than the last. When the coffin has been destroyed an item will drop out, and here's the bit KS'ers love best. First to nab the item practically has the game in the bag, but there is one final challenge. Now that you have the item you need to go ALL THE WAY back again! And don't forget that all this time you are being completely battered by these level 100+ mobs in every nook and cranny they can reach.
If you make it all the way back you recieve an item. I don't know what item it is but I've heard rumours that it's a Chaos. I mean a Chaos... honestly, anyway, this map is far-off in Global MU so I'll leave my bibliac post there.