Exodia the Forbidden One: Exodia is a combination of five separate cards that, when assembled, allow the player to win the duel instantly.
Dark Magician: Dark Magician is a classic card with high attack power and versatility, and has been featured in many different versions and variations.
Blue-Eyes White Dragon: Blue-Eyes White Dragon is another classic card with high attack power, and has been featured in many different versions and variations.
Chaos Emperor Dragon - Envoy of the End: Chaos Emperor Dragon is a powerful card that can destroy all cards on the field and inflict damage to the opponent equal to the destroyed cards' attack points.
Yata-Garasu: Yata-Garasu is a powerful card that allows the player to draw a card and then force the opponent to discard two cards, potentially disrupting their strategy.
These are just a few examples of the many powerful cards in Yu-Gi-Oh!, and the strength of any particular card can depend on the deck and strategy it is used in.