You're paying 4B to start with, and then you also have to sacrifice a creature with high power to make X a relevant value
Theyre powerful, rare, and were initially bound by the single-card rule meaning there could only be one of them per deck
Ironically, this massive popularity probably prevented the card from seeing more play in tournaments, as players who might have tried to reach for the Queen instead decided to cash them in for other cards they needed more
I think you usually will want to pay the full five, because that gives you the option of using his -4 right away, and thats an ability that will usually allow you to kill something
While its a bit niche, its perfect for players who love to have silver bullet answers at the right moment, especially in control shells