Hey there,
I'd also like a card... well, it is already scripted, but it needs to be fixed.
I'm talking about the good old divine serpent.

I know it's impossible to create actual infinite ATK & DEF, but here are effect-style workarounds:

1. Can't be destroyed by battle while in DEF position: It's logical, because you can't go over infinite DEF points.
2. Neither player takes battle damage from battles involving this card: Also, you can't pierce over infinite DEF or go over infinite ATK. It also deals no damage to the opponent, but activates one of the effects below dependent of the type of attack.

It's anime attacke-effects:
3. If this card destroys a monster by battle, your opponent takes damage equal to the destroyed monsters ATK.
4. If this card attacks directly, at the end of damage calcualtion: Reduce you opponents life points to 0.

And then there is the fact that you can still lose to exodia, final countdown etc.
I really don't know how to fix this. However, most cards that prevent loosing only do it if your Life Points hit 0. Maybe you can find a workaround this way?

Greetings
VB99

EDIT: Fixed according to StormWind0's information.

If I remember right on that last one.  It only reduces LP to 0 on direct attacks if they go through.  As for normal battle damage it was equal to the destroyed monster's ATK I think.

Really? Well, if you say so, it's true, I guess.