Remember in the original days of Yugioh how "Blue-Eyes White Dragon" was the top monster card? One of the first Ultra Rare cards to exists. Now however it's printed as a common card in the "Dragons Collide" structure deck. Back then this was the card that when someone were to summon it you'd be like "Oh crap, what do I do now!?". Till this day it is to my knowledge the most powerful normal monster.
And now we go to "Yugioh Zexal", the latest edition to the franchise. In this series they've introduced "Galaxy-Eyes Photon Dragon", the latest of the deadly monsters. It has the same atk/def, attribute, and type as "Blue-Eyes White Dragon". However, it is way better than "Blue-Eyes". It's effect allows it to be special summoned allowing you to normal summon afterwards, and it's nearly impossible to defeat in battle. On top of that, it's an "xyx monster" killer due to it's effect to get stronger after battling and xyz monster that still has it's material attached to it.
I know there are thousands of deadly cards, but I'm only discussing the most popular ones from the show. Galaxy-Eyes is a great replacement for Blue-Eyes. I only wonder what will they come up with next.