The flexibility of being able to choose a value for X is great because we might have an early-game case of wanting (or needing) to cast it for X of one or two, or we can wait until late-game and sweep a much bigger battlefield
For context, Hop's Zacian-ex from the sought after Japanese Battle Partners and English Journey Together set has an attack that does 240 damage, and with this Tool alone it can now one-hit knockout a ton of meta-game threats that it faces, such as Bloodmoon Ursaluna-ex
At the beginning of your upkeep, put target creature card from a graveyard onto the battlefield under your control
Both benefit from [c]Jace, the Mind Sculptor[/c], [c]Stoneforge Mystic[/c], [c]Thoughtseize[/c].....too many cards to list
This is meant to represent Prosper's connection to strange, otherworldly planes and triggers off of plenty of red impulsive draw effects
They are some of the most powerful cards available in the game