Next expansion WAR idea for skill

Imagine an attack so bad-ass and epic, tanks will go fan girl crazy over it....

Good evening, i have been carefully thinking about a way to expand the WAR arsenal of abilities even further. This ability would be the lvl 90 skill and is called RAGING BEAST; this ability would be a single use gauge ability that would fill up over time as damage is taken. Once the gauge has filled to 25% or achieved a stack of 1 out of 4, the player is able to use an earth shattering AOE attack with a potency of 300 for every stack maxing out to 1200 potency!!! Being an AOE type attack it would hit its main target for a max output of 1200, then hit any other enemies around for a decreased potency of 650. The attack itself would replace Decimate/Chaotic Cyclone when activated giving players the ability to have 2 separate gauges for increased DPS output. In addition to this it would also reduce infuriate timer by 15 when cast at full power 4/4.

Now a question that needs to be addressed is how to calculate the rate at which it fills?? I am no programmer so i couldn't give you exact numbers calculated out, but i would say it grows by a crazy way i came up with. So lets say the player has taken damage equal too 10000 that would then be divided by 15% equaling out to 666(mark of the beast, beast gauge see where i'm going with this) that then is multiplied by .15% to give a gauge rate of 100 or 1%. So if my math is correct for 100,000 dmg the WAR is able to use an attack capable of doing decent dmg to large pulls and single targets. Something that can be used enough times to neither be forgotten or overused too much by my calculation.

Visually it would be an epic looking attack, as the gauge fills the WAR begins to visually become enraged. My initial thought is to have their left arm/hand begin to glow almost like a flame is growing composed of aether. Once triggered the flame would then transform into a burning axe (similar to a lvl 1 axe for a simple yet badass look). The attack would have the WAR jump up in the air spinning as he ascends, once peak height is reached they have their main weapon in the right hand and a burning aether axe in the left. As they descend they give out what looks like a roar as the attack hits the ground giving the visual of a burning eruption, somewhat similar to the way WAR lb3 looks. The AOE would then engulf the same area as that of its predecessors AOE attacks.

The idea is simply the next stage of berserk for WAR, one which would tie in with the title Berserk and expand on its abilities. The backstory i have come up with is over time Broken Mountain has regained his powers and has obtained what appears to be an enraged form, a form capable of unleashing ones pain and suffering into the form of an attack. It is perfect for Broken Mountain to be the one to introduce this attack as he doesn't really utilize an axe but rather a grimoire. its an awesome way to introduce it as opposed to Curious George or Dorgono, who both gave us a cool intro to new attacks.