Now if i have to change the thread name with Demise Shadow| Demise Shadow?
Though I am one of those who agreed that camoninja's idea was somewhat better than your own, you are free to choose your own card names as you feel appropriate. He felt that the card's ability seemed better with 'demise' instead of 'death', but if that is not the case for you, and you have a pretty good argument / feelings about your card name / art, don't worry about that part
I'm not that much into the mathematical equation of this ability, but I would say max damage at 20 or 25 would be most appropriate. Currently there are 0 cards that can do 30 damage, excluding heavy armor + rage pot on any creatures or overdrive + gravity creatures, but at 20, it is realistically similar to dragons, except better since you have to wait quite a bit for the damage to reach that high.