They open up design and player decision-making in a way that a morph of early versions of the planeswalker idea, sagas, dont, since they take the basic planeswalker idea and give it turn-based gating
Monstrous Rage at 56%, Cori-Steel Cutter in 43%, and so on
Priest of Titania This 2-drop common defines the Elf Archetype
Roiling Regrowth is the safer version with a lower floor, and Entish Restoration has upside if you control a large creature
When you actually read it though, you realize that it's a Crucible of Worlds with hands that your opponents will catch
If the number of differently named lands you control changes while activating mana abilities (probably because you sacrificed one or more lands), the cost to activate the ability remains what you previously determined