The big selling point is that it kills a commander on ETB
It's a game-ender, typically sweeping away your opponent's entire board, while preserving any colorless permanents you've chosen to play, and, more often than not, also leaving Ugin alive to keep pecking away with their +2 damage-dealing power
Compared to Downard Magician, which plays a similar role, it does not require a cost, but can only be summoned in Main Phase 2, and can only use Xyz monsters of rank 3 or lower as a material
How Many Cards in an MTG Deck
Notably, Porygon has two evolutions introduced in later generationsPorygon2 and Porygon-Zwhich extend its presence across multiple regions and games, including Kanto, Johto, and beyond
That means this card was kept under wraps for nearly a decade