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I take these repeated questions as a hint that I need to give more info on some specific bosses.
For Valithria, you want to equip as much stamina gear as possible, get two fast low level weapons (level 1 whites do the trick, or thunderfury, whatever), get close to valithria, and attack.
do not put diseases or the mobs will die too quickly, just spam heart strike in there. you should always be attacking something.
spam vampiric blood on cooldown.
your kill priority should be suppresser > lich > blazing skeleton > rest.