So Edward has give the idea for 255 bosses who drops necklaces/rings/trinkets etc...
i'll suggest you to make 2 kind of bosses as i said before 1 for these who have just reached 255 and are not that strong to handle on big bosses and 1 for these as me who have already got everything possible and waiting for new challenges make their difficult balanced so be possible to kill. And one more idea given from another player forgot the name to put nice effects on items can't give an example now but you have a full working team to get on this idea
Sorry for bad english