How to participate?
There are 8 levels of Blood Castle in the game and you can enter depending on your level. You can participate in the event by crafting an invitation first.
You need Blood Bone, Scroll of Archangel (dropped from mobs, both need to be the same level as the BC you are trying to get into) and Jewel of Chaos mixed in the chaos machine. Success chance depends on server settings.
You can check for which level of BC you are by typing /entries in the MU chat. This will also show you the daily limit of participating in events. Finally, to enter the event you must go to "Messanger of Archangel" NPC either in Lorencia (bar) or Davias (church) and select the corresponding level of BC.
How to play?
The main goal in the event is to take the quest item which drops from the statue and give it to the fallen angel.
There are few stages. First you need to kill monsters so you can get to the castle gate. The count depends on the players participating in the event - 40 monsters per player. After you kill the monsters and destroy the gate, you can enter the castle room. There you will have to kill specific monster "Magic Skull". Again, the count depends on the players participating in the event - 2 monsters per player.After you've killed the requiered magic skulls there is one last challenge - to destroy the Statue of Saint which drops the quest item, an archangel weapon.
The final step is easy enough, you return the weapon to the fallen archangel. There are 2 NPCs for you convinience - one at the beggining of the map and one in the castle room.
Notes:
Keep in mind that the player (party) with most damage will get the weapon from the statue so you need to be careful. Only one party will get rewards for returning the quest item.
BC is mainly used for experience (and rewards if you're the lucky party). Good spot for experience is right infront of the castle gate as there are more mobs than the room.
Buffs from pumpkins are really useful for BC if you are not that strong.
You can set up mu helper to pick up parts for invitation by adding "Blood +X" and "Arch +X" where "X" is the desired level of BC. Blood and Arch are just an example, there are many more variants of the item words but this will do the trick.
What are the rewards?
Rewards depend on server settings but they are usually jewels, old boxes, demon or angel.
Useful links
PHOENIX
Details about server - check Events Info section
Events Levels Entries
NONRESET
Details about server - check Events Info section
MAX50RR
Details about server - check Events Info section