Door of Destinies is a four mana Artifact where you choose a Creature type when it enters
Creature - Vampire Color tag templates(None) Yahenni, Undying Partisan Haste Whenever a creature an opponent controls dies, put a +1/+1 counter on Yahenni
It reduces only the generic component of that cost
That win condition is a particularly popular one in the Commander format once infinite mana has been assembled
I will admit, it is a good bit of work at the beginning and does require a bit of upkeep (adding new, deleting old, editing, etc.), but the payoff (building teams without ever handling a figure, and changing decklists on the fly) is amazing to me
The -1/-1 effect ranges from being a minor nuisance that takes out a few mana dorks, to a full on board wipe depending on which stage of the game Phyresis Outbreak is played in