Unfortunately still didn't receive Sacred Unicorn. Why is it so I can't imagine.

Due to probability and fact that a chance to draw a legendary card is only (if I remember correctly) only 0.8%. Thus you should expect around 8 legendary cards in 1000 reward cards, but it might as well be only 4 but as many as 15 or so. Again, probability!
Ruler and Lord are twice more expensive, so better to draw one of these! You can have two unicorns for one of them.