They can be surprising ... killing meph is like the moat trick, so he can be like less of a danger .. and if one is kind of underleveled and undergeared, and if there are like 5-6 of those blood lords .. and they start tossing fireballs and meteors at once, they can hit pretty hard. And you want to open that goddamn chest ^^ so that can be a little bit of a danger point, at least in hardcore. And they have that pesty 50% or something damage resist, they are a bitch to kill.