While not as oppressive or powerful as Sliver Queen or Sliver Overlord, it plays an exciting game nonetheless with options to be built competitively or casually
The death trigger is highly relevant, since as part of the 99 you don't have to worry about it staying dead for long, and as your Commander you almost never have to pay the commander tax so you can build around the card without worrying too much about it
Im not sure why it doesnt work with commanders, but there are plenty of other targets to choose from
These groups are not tied to any particular archetype or strategy, but they provide a specific experience or fulfill a need that most players seek
3: Target creature you don't control phases out
Undead Servant is definitely below the curve, and despite the potentially high upside (which gets higher in Limited since you can run as many as you want) it wont always be worth playing