Here's why:
* Obelisk the Tormentor is a real card from the "Yu-Gi-Oh! Trading Card Game" (TCG). It exists as a physical card you can buy and play with.
* "Silfer the Sky Dragon" is a fictional card from the "Yu-Gi-Oh!" anime and manga series. It was introduced as one of the three Egyptian God Cards, alongside Obelisk and Ra.
While the anime popularized these cards, the actual TCG has never had a "Silfer the Sky Dragon" card for players to use.
However, there are a few things to note:
* "The Winged Dragon of Ra" card is a real card in the TCG and represents the third God Card from the anime.
* "Silfer the Sky Dragon" has been featured in other Yu-Gi-Oh! games, like "Yu-Gi-Oh! Duel Links" and "Yu-Gi-Oh! Master Duel", allowing players to use it virtually.
* There have been several cards with similar effects to Silfer in the TCG, like "Cyber Dragon Infinity" and "Number 81: Superdreadnought Rail Cannon Super Dora."
So while there isn't a literal "Silfer the Sky Dragon" card, its influence and design have inspired many cards within the real game.