Dependant on the hero's HP?
If so
455/520*100 = 0,875 * (8*25) =175
If so
Code:
In your example if your hero is at full health this would do 200 damage he takes 65 damage bringing his health to 455<damage formula>
value = (($gameActors.actor(your hero id).hp / $gameActors.actor(your hero id).mhp))*($gameActors.actor(your hero id).atk*25);
<\damage formula>455/520*100 = 0,875 * (8*25) =175
Nice! ...but not completely.
DEF influence still needed and it will be perfect.
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After some more testing still its no good. You see, stats like ATK and DEF wont change ingame (just rare exception with +- 1 or 2).
And with this formula battle with 5000 HP will be looooooong.