Background: Alendyias is a world that was formed inside the Fracture of Reality, one that is still forming as the Fracture in Reality grows and absorbs other worlds in its path. Absorbed worlds and all life in and on them are saturated with Chaos Energy, which in many cases turns ordinary creatures into monsters like trolls (formerly large apes) and goblins (monkeys).
Chaos energy and magic go hand in hand (are practically synonymous), so various creatures have turned the Chaos Energy infusing them into something we call Enchantments, a magical effect they hold during life and grant to whatever kills them upon death. (The link explains how this works for one specific monster, a slime-type creature called a Plop.) Enchantments are not just imposed by the Fracture, they are reflections of a creature's innate nature. If a creature evolves in such a way as to develop a new nature, it will develop a new Enchantment as well.
The trouble is, I need a creature with the Knockback enchantment, as this is a very useful Enchantment. Knockback is (sort of) simple; items and creatures with Knockback absorb kinetic force when struck and put it into their pushback. In clearer terms, due to Newton's Third Law, all matter pushes back with equal and opposite force when pushed upon. All Knockback does is redirect the force acting upon it into the force it is putting out, essentially doubling an item's kinetic output to push the offender away.
Enchantments are based upon a creature's nature and/or physiology, so a creature with Knockback would need:
Elasticity-In order to absorb and redirect force for Knockback, the creature must have some inherent springiness. This could come from blubber, springy hide, or inherent rubberiness (like Plop).
Nature-In order for a creature to have Knockback, it needs to use its inherent springiness to knock enemies around, tackling, shoving, and pushing things with its springy body. I'm thinking something like a headbutting beluga. This entails aggression, a certain vindictiveness; to push back when pushed, to strike back when struck.
Why am I asking this? Well, I could just handwave this thing's existence, but all of my other creatures have a logical basis, so this Knockback monster needs one as well. Thus, my question is How Can a Creature With Knockback Come To Exist?
An answer must determine a creature that could evolve to meet the specifications above; ie. one that has the potential to either gain Knockback upon entering Alendyias or could evolve to have the Knockback enchantment.
An answer must also determine how the said creature would need to evolve to gain the Knockback enchantment and what conditions are necessary for making it happen.