This is a removal spell that will make the target creature get -5/-5 until end of turn in Magic: The Gathering
However, like self-mill, this can have a psychological effect on newer players, which may be holding it back or be the reason why we so little of it at common
The long and short of it is that Izzet decks often care a lot about being able to switch between controlling and aggressive roles, and Restless Spire is a rancid blocker
Set Six Emerald And Sapphire Starter Deck Azurite Sea Big Hero Six plays a big role in this starter deck as the whole crew has at least one card variant tucked away in this Emerald/Sapphire deck
This is a specific strategy which requires a lot of niche cards to work, so you get some uniquely powerful rewards in the mix, and that can be fun for a lot of players
Free counters, surgical one-mana answers, and the stack interaction that stops every combo line in cEDH blue brings the control that protects your wins and shuts down theirs