They are on a rotating schedule, so they will all come back eventually. If you have a specific one in mind let me know and I'll give you an approximation of when it will return.
Hi mi7ch, Thanks for the response! I have been in the game (ZS) for 263 days and have seen all the RAIDs except the following: UNdead, Abdominal Snowman and Nuclear Engineer. Thanks, these are the only ones that I don't have any achievement on at this point.
A belated welcome to the game, then! The Snowman will be Feb's Raid Boss with the other two following shortly after that, although they haven't been assigned a specific month yet.
WE SERIOUSLY NEED TO SET THE MINIMUM REQUIREMENT FOR RAID. CAN BE EITHER LEVEL OR HOW LONG HAS JOINED THE GAMES. CURRENTLY NEAR ALL RAIDS HAS IT PARTY KILLED. THE CULPRITS IS ALWAYS NEWBIE WITH ACCOUNT NEWLY CREATES. NOT SURE IT WAS ON PURPOSE OR WHAT, BUT THEY ALWAYS SCREW UP AND SPOIL THE FUN. I SUGGEST LEVEL 50,75 OR 100 AS THE LOWEST LEVEL FOR RAIDS. battle arena has min requirement level before can participate, newly create faction need to wait few week before can join the war, so why not put some lowest minimum requirement for raids?
When is Kano going to make it easier to get these darn keys to open RB's!! 4500 energy just to open it, now i can't even attack and heal it, what's the point.
maybe instead of wasting valuable energy to get them why not just sell them for x fps easy then buy key do raids and not waste energy trying to get them