Repeatable creature destruction isnt terrible, otherwise, no one but nostalgic boomers would run Royal Assassin
But just having the card isnt enough
While Ive mostly seen it in Tron strategies, you can run it in other similar decks where you want to access card selection at instant speed
Invasion of Moag F-Tier: Solid support for the +1/+1 counter theme in March of the Machine limited, but constructed has cards like Brokers Ascendancy and Felidar Retreat that can put a +1/+1 counter on our team every turn, which is way more upside than potentially flipping into a 3/3 creature
I wasn't sure if I wasn't using the right separator for the 2nd question or what
The design of Starfield of Nyx takes the design a step further by adding a triggered ability that gets enchantments back from the graveyard, and then adding a threshold limit to turn on the static ability