all the buffs work, they just have shitty values on classic, this was discussed a lot of times before couple of months after server opening. the value is so small and the damage from skills its so random that is hard to notice the influence of this skills in classic. anyway i pulled out some testing with higher damage values where its easyer to understand that they do work. Death spike on target no buffs. Same targets same gears same chars, death spike on Resist Dark buff same with death spike on song of invocation. now with holy resist. same characters, first print no buffs. second print with holy resist. again due to the fact the damage of skills is so random its not so easy to understand but you can see when buffs/song is on the damage is slightly lower.