The fact that split cards change whether its in your hand, graveyard, or on the stack is important because of how rules consider each spell
The Eldrazi were the first nail in the coffin for Progenitus being generally easier to get out and offering more utility and power once out
Dont forget that Azula is blue, so you can flicker it for more card advantage and removal
You can find showcase legendary cards in Draft, Set, and Collector Boosters as well as within products that contain those boosters
The two cards play together reasonably, with their mana costs playing a role in illustrating the fact that theyre going to slot into slower archetypes
Zero Point Ballad This is basically a modern Black Sun's Zenith for one less mana, but there are no counters, so it has no effect on any creature you don't kill