Killed him last night with a group of 4, one 65 cleric (me), 65 SK (Vishus), 65 Enchanter (Silverspell) and 57 druid (Otter). Took a while for us to kill him, he was unslowable via enchanter slows and he dropped a Shadowflame (alas I forgot to take a screenshot of it but she was hitting for an average for 260 with it and had some hits for 280, non-crits. As soon as I can I'll update this with the stats of the sword, it was a very very nice sword. Probably wont be until tonight though, I do recall that any class that can use 2hb can use it and it was no drop (which surprised us at first as only Boss loot (Korocust) in HoB was no drop and everything else was tradable).
One thing about the Spiritmaster, he doesn't seem to have a PH. After we cleared out the room we found him in, his spot didn't respawn a PH while the other two spots respawned kobolds again. (Note: you can use WoT to pacify the other two spawns so he can be single pulled. However he is immune to WoT, too high level for it & didn't test out Pacification.) So he might be on a timer like the minibosses in BoT where the spawn in the same spot but at relatively fixed intervals.
Shadowflame
Magic Lore No Drop
Slot: Primary
Skill: 2H Slashing Del: 44
Dmg: 41 Dmg Bonus: 45 (for a 65) AC: 10
Magic Dmg: 2
Skill Mod: 2H Slashing +3%
STR: +12 STA: +10 WIS: +10 INT: +10 HP: +60 MANA: +60
FR: +12 CR: +12 MR: +5
Recommended level of 51.
WT: 9.0# Size: Large
Class: WAR PAL RNG SHD
Race: ALL
Edited, Thu Aug 7 14:08:38 2003

Fleshsear Cleaver
Ring of Firewarding
Shadowflame