[PvK]

The results are not guaranteed, but it can be an extremely good deal. My two recent castings yielded:

Undead Commander, Mage (W1E3D2), Mage (W2E1D1), 25 unfrozen)

Undead Commander, Mage (W3E1D2), Mage (W1E2D3), 17 unfrozen)

This is a W3D1 spell (which one could easily boost up a W2D1 or even W1D1 caster too... e.g. a Spectral Mage which is D3, so e.g. anyone with D2 and a skull staff). So it gets you mages up to E3 and possibly from D1 to D3, and also combined into a single caster so you can get to spells like Streams From Hades, Catoblepas, Blight, Claymen, Ghost Ship, Leviathan, forge Jade Armor, etc...

The plain fighting ability is worthwhile, too. Mixed with a bunch of regular undead, the troops' cold aura alone could be a force that could be quite potent simply by freezing enemies.

In other words, it can open up lots of useful paths and combinations, and other good things, so it is worth it, just maybe not always.

PvK