Naban, Dean of Iteration One of the first typal cards on the list, Naban, Dean of Iteration is the epitome of niche but powerful
This does not count creature types exclusive to Un-sets
If you're playing Aristocrats, Mill, or Reanimation, or can produce infinite black mana in some way, he's likely going to be one of your win conditions
Once it resolves, it becomes an artifact permanent
While Drain Life only lets you target a single player, you can switch it out for cards like Exsanguinate or Debt to the Deathless, which can make all of your opponents lose life
If your goal is to attack often you can look for commanders like Isshin, Two Heavens as One and attack triggering cards like Inti, Seneschal of the Sun, Hellrider, and Beastmaster Ascension