Text (7th+errata): 1/5, Defender. ; {2}{U}{U}: ~this~ gets +4/-4 until end of turn and can attack this turn as though it didn't have defender. [Oracle 2005/08/01]
Paying to make the Wall capable of attacking does not override the normal rule that a creature may not attack unless it began your turn in play. [Duelist Magazine #2, Page 9]
You can apply the +4/-4 bonus as many times as you have mana to pay for it. Of course if it does not have enough toughness, it'll die. [Aahz 1994/06/16]
Extended tournaments (see Rule 913) banned this card from 1999/10/01 to 2001/05/01.