Most of the cards banned in normal play are all cards that mill or allow you to shuffle cards out for more cards. For example, "Pot of Avarice" is a spell card that has the following affect:
"Target 5 monsters in your Graveyeard; shuffle all 5 into your deck, then draw 2 cards".
It is banned for the sheer fact that it saves you if you have a monster in the grave that you want back or like to use. If a card that allows spells back to the hand is paired with this, it could go on forever, basically making his deck appear almost endless. In a unofficial tournament (meaning everything was allowed), I faced a deck that used "Pot of Avarice" in a Dinosaur deck featuring "Rescue Rabbit". it was relentless. 3 pots plus the continuous rabbits put 4 Xyz monsters on the field in less than 5 turns.
Of course, there are some banned cards I don't understand. For example, "Card of Last Will" has this effect:
"If the ATK of a monster you control becomes 0 by a card effect: Draw until you have 5 cards in your hand."
Why ban that? First of all, Reptilianne Gorgon and Reptilianne Poison are the only cards that I know do that effect, and secondly, what is the big deal with tossing a hand for another that may or may not be good? You're basically asking for the guy to find a quick way to trash his hand for some other cards that may be worse than what he had. That seems like potential suicide to me if you get carp on the redraw. It's like the lottery. Besides, if he doesn't have 5 in his hand, say he has 4. What will one card do?
"Target 5 monsters in your Graveyeard; shuffle all 5 into your deck, then draw 2 cards".
It is banned for the sheer fact that it saves you if you have a monster in the grave that you want back or like to use. If a card that allows spells back to the hand is paired with this, it could go on forever, basically making his deck appear almost endless. In a unofficial tournament (meaning everything was allowed), I faced a deck that used "Pot of Avarice" in a Dinosaur deck featuring "Rescue Rabbit". it was relentless. 3 pots plus the continuous rabbits put 4 Xyz monsters on the field in less than 5 turns.
Of course, there are some banned cards I don't understand. For example, "Card of Last Will" has this effect:
"If the ATK of a monster you control becomes 0 by a card effect: Draw until you have 5 cards in your hand."
Why ban that? First of all, Reptilianne Gorgon and Reptilianne Poison are the only cards that I know do that effect, and secondly, what is the big deal with tossing a hand for another that may or may not be good? You're basically asking for the guy to find a quick way to trash his hand for some other cards that may be worse than what he had. That seems like potential suicide to me if you get carp on the redraw. It's like the lottery. Besides, if he doesn't have 5 in his hand, say he has 4. What will one card do?