[Shovah32]

The umbral is far superior to a black sevant.

Umbral:
68 Health
22 Strength
12 Attack
12 Defence
15 Magic Resistance
20 Morale
14/3 Movement
40 Normal Leadership
Amphibious

Black Servant:
18 Health
13 Strength
11 Attack
11 Defence
10 Magic Resistance
17 Morale
12/3 Movement
No Leadership

Both are undead(umbrals MR alone makes it superior due to this), both have 100% cold and poison resisance, both have stealth+0 and are ethereal.

So yes, imho Umbrals are that much superior to black servants.