Winged Dragon of Ra's Attack and Defense Points
Winged Dragon of Ra has a special ability. Well, it has a lot of them. But the important one is this:


  When this card is Normal Summoned: You can pay Life Points so that you only have 100 left; this card gains ATK and DEF equal to the amount of Life Points paid.


So if you're at 3,500 life, you can choose to activate this ability leaving you with 100 life. Winged Dragon of Ra would then have 3,400 ATK and DEF, representing the 3,400 life you paid.

If you choose not to pay, then he enters as a 0 0. You can still activate his kill ability, although consider that you have to tribute 3 monsters to do it, so to even that out you'd have to pay 3,000 life. He's definitely a card you build around if you're going to play him.