Well you know that in GMS holds a event called "Day of Darkness", well we should call it "Day of Catastrophe" (or does that sound to cliche, well any who)....This command is fairly easy in my opinion, !dayofcatastrophe is the added command, summon the black boogie (which should drop rare weapons, such as the crimsonwood weapons), few bosses, dark monsters and a notice which says [Notice] The monsters of the dark have been in the shadows, now have risen in numbers to attack the noobs ;D (or something like that)...
Well hope you like it sorry if it isn't in full detail, rushed version because going to school in 10 minutes.
~GaiaAero