To help me out on this, what kinds of "Special" cards would people like to work their characters towards?

Example: Yugi starts with his grandfathers deck where Dark Magician is his prized monster, but Dark Magician isn't exactly the be-all-end-all of power. Eventually he manages to unlock the powers of the feared Egyptian God's. And when the God's are stolen from him, the mythical dragon Timaeus grants him his power to defeat the ancient threat of Orichalcos.

So, the "Special" cards for Yugi would be the Egyptian God's and Eye of Timaeus.

Also, would people be interested in saying that the reason that they can even do what they do in this world is because of something like the Millenium Items? Or maybe the signs of the Crimson Dragon?

Pretty much, some advice on "Why the gang are as super special awesome as they are?" Would be helpful.