An interesting idea!
While this skill seems to have aspects of Beserker (damage increase based on low health, Damage-taken increase after using a burst skill) it also has aspects that are not helpful or usual for a Beserker kit (knockback can be less than ideal depending on which part of your combo you are in, and Beserkers do not "explode").
This needs more from both the Lore and the Playstyle elements of the skill.
Lore: Explain the Beserker Explosion more in-depth. Do not worry too much if you can't, someone can.
Playstyle: It is rare that Beserker would want to knockback an enemy far, unless the enemy was incapable of kiting. Even so, this skill has the feel of a 'Warm-up and Burst' class rather than a 'Tanky Melee Dps'. Please justify this skill's placement within the skill set.
First of all, I was thinking that wrath be a skill without any warm up/casting time. It would just be an explosion that a berserker can use while running. So about the "explosion", I really have no better way to explain it, let's just say, that berskers can release an explosion out of anger... I guess? I'm probably thinking about like how characters in any fiction/fantasy anime, such as dragon ball z can release bursts of energy that blow back enemies... I honestly dont know XD
About the playstyle, to be honest, I was not thinking about this, and didn't consider the negatives about the knockback effect. However, now that I think about it, I'm thinking that it might be kind of useful in group fights. For example, since berserkers are tanks, they would most likely be in the front lines and go in first. I was thinking that wrath (suggested skill) could kind of have a scatter effect, in which enemies would be left split from their teammates, and the team that the berserker is on could single out important targets. I feel like wrath may work well with the skill, toss as well. For example, lets say a berserker got in close range with an enemy caster or something. The berserker would be able to use toss on the caster, to prevent him/her from escaping, then wrath afterwards to blow back and deal damage to any allies of the caster that try to come help.
I have no idea as to how team fights work in herocraft, so what I just said may not really work at all