Lich is by far more dangerous that Shiro on HM...
Wait, really?
First, I do realize that the original post was made in June. I just want to post this up for future reference

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As for the mission, I actually found it easier on HM than on NM because of all the extra PvE skills and heroes I had access to when I came to do it on HM. The builds I used (as an ele) was centered mainly on single target lockdown, damage and blind. I can't recall it exactly, but it had had something along the lines of... Blinding Surge, Lightning Orb, Chain Lightning, "You move like a dwarf!", Ebon Vanguard Assassin Support, Gale or Lightbringer's Gaze, Air Attunement, GoLE.
Although those knockdown skills above will have no effect on Shiro by themselves, the ritualist skill Earthbind will make him vulnerable to them. With this in mind my hero setup was two ritualists, one Signet of Spirits restoration support and the other a Reclaim Essence spirit spammer with Earthbind and Shadowsong, and an MM Bomber with Aura of the Lich (you can use other elites). I used the Illusion Henchman, Odurra, (VoR, Empathy) Cynn, (Herta is also a good choice) and Khim and Mhenlo to make up for the loss in healing power to make up my 8 H/H team.
There is enough damage to make it through the ordinary mobs, and once you get to the two big bosses, they will be unbelievably easy as you'll have them groveling on the ground with your skill setup. Paired with the armour ignoring DPS of your spirits constantly taking Shiro/Lich down, it should make the mission a breeze.