A Blue Eyes Chaos Max Dragon attacked my face down Marshmallon, which subsequently flipped him face up inflicting 1000 damage to the opponent, then the effect of Blue Eyes Chaos Max Dragon activated (which with double piercing battle damage I should've taken 7000 damage), that then caused me to activate Dimension Wall (to make my opponent take the Battle Damage I would have taken as a result of this battle.) To which I was surprised to find that it did only 3500 damage to my opponent. I've checked all of the rulings, and I'm pretty sure that Dimension Wall is supposed to make him take that 7000 damage I would've taken, instead of the 3500 damage it did.  regarding Blue Eyes Chaos Max Dragon and battle damage:
Q: It is a turn during which the effect of "Action Magic - Full Turn" is applying. If my face-up Attack Position "Blue-Eyes Chaos MAX Dragon" attacks my opponent’s face-up Defense Position "Sentry Soldier of Stone", what is the resulting battle damage?

A: "Blue-Eyes Chaos MAX Dragon" has an effect that inflicts battle damage to your opponent equal to twice the difference between its ATK and the other monster’s DEF when it attacks a Defense Position monster. In this scenario, the 4000 damage (twice the difference between its ATK and the DEF of "Sentry Soldier of Stone") is doubled by the effect of "Action Magic - Full Turn", and inflicted to your opponent. (In this case, your opponent takes 8000 damage.)

Thank you for your help, and hopefully you guys can get to the bottom of this [:smile:]