The lighting (torches in the tower) in Deadwood. The birds in Deadwood. The "darkness" effect in Deadwood and other certain areas. Fireworks. Heh, Deadwood.
Please, please, create an option to disable all those things the same as the way image animations are disabled. This option would bring new life to Deadwood, Snow, the caves, guild houses, etc. as people would no longer avoid them due to immense lag.
Maybe even a third option, to disable the ganis such as juggle etc.