Tamas didn't participate in the battle, because he is currently in the middle of a research. In the cave where Sam was stationed, there was a tunnel leading to another cave in which Tamas is currently stationed and is actually looking through different dead bodies.
There are some high level necromancers that realize as much quantity of undead give them advantages, the quality of utmost importance, so they change the bodies of the undead, they take different paths, based on their studies.
There are some people who use poisons and toxins as enhancements, some people that attack special hidden weapons to the undead with some hidden mechanisms inside their body.
Some people that replace the skeletal network with different metals, some modifying the flesh using different experiments.
Tamas style of study is very different he actually got an epiphany before they reached the Merene family, so he was excused from fighting in this battle.
