Ghostly

Stat	Normal	Nightmare	Hell
% Base Life	300	250	200
% Base Experience	300	300	300
+% Attack Rating	67	56	49
+% Damage	90	75	66
Minimum Cold Damage	[MonLvl*33/100]	[MonLvl*33/100]	[MonLvl*33/100]
Maximum Cold Damage	[MonLvl*50/100]	[MonLvl*50/100]	[MonLvl*50/100]
Cold Length (Seconds)	6	6	6

[1] [2]

• Easily identifiable since they are translucent.
• Cold damage does not increase with player count, but a critical hit will double it. [3]
• Set to Damage Resist 80%. This even applies to Immune to Physical monsters: although Immune to Physical will still be displayed, physical damage will harm them, and DR -% applied by Decrepify and Amplify Damage will be 100% effective, not 20%. [4] [5]

Although the Barbarian War Cry's physical damage obviously doesn't damage the Immune to Physical Champion Blood Lord, it does damage the 'Immune to Physical' Ghostly Blood Lord since it has actually been set to DR 80%.

Reference

• Special Monster Bonuses (Arreat Summit)
• Which elements are most resisted in Hell? (Technical Discussion)
• Nefarius, Boss Status Modifications (1.11b) (Phrozen Keep)
• Onderduiker, Monster Bonuses, Death Damage and Corpse Explosion (Technical Discussion)