While some of the cards on this list, now five or ten years old, may be unknown to newer players and have faded a bit in the eyes of long-experienced ones, many of them are still format-defining not just for what they did in-game, but outside of it as well
Having a way to deal with a problematic permanent when you need to and a creature to threaten life totals with when you dont is phenomenal
You may spend mana as though it were mana of any type to cast creature spells
Instant Copy (CTRL to add secondary) Draw Commence the Endgame This spell can't be countered
Asinine Antics Not only does Asinine Antics nerf all opposing threats, but it also floods the board with cardboard rectangles
Its after all their signature mechanic, and no other creature in the entirety of the Multiverse has it but the Oh, wait