You don't need a spell at all.
Use Phoenix Dive/Vault/Tactical Retreat/Teleport to get up onto the pedestal with him
Use Teleport to teleport him off the pedestal.
Attack a party member with Right Click + Attack or if you have the attack action bound. Do this repreatedly so as to "race" the physical armor regen. Once you start doing vitality damage, they will leave copious pools of blood.
Either position the blood balloon character right next to him and get a little bit lucky with the splashes
Make a blood pool and teleport the Historian into it
Cast bless on him, the ground, on everything until it completes it.