If an item kills a Whackagi, then it gains the Strengthen enchantment. The Strengthen Enchantment ups an object or material's rigidity (capacity to hold a shape without deforming), tensile strength, shear resistance, and so forth by 3 times, then 5 times, then 10 times.
In simpler terms, the Strengthen Enchantment makes an item 3x harder to bend, deform, shatter, shear, snap, weaken, or break in any way upon first killing a Whackagi. The second time that same item kills a Whackagi it will become 5x harder to bend, break, or weaken, and the third time that item kills a Whackagi it will become 10x harder to bend, break, or weaken. Note: This Enchantment does not increase the weight or mass of an object, just its resistance to damage.
Furthermore, an item with the Strengthen enchantment also multiplies the force put into it by its owner (the person who killed a Whackagi with said item), causing it to hit harder. Great Enchantment, right? There's only one problem. An item or creature must kill a Whackagi to get it. And Whackagi, thanks to their rubbery physiology, are just about invulnerable to medieval weaponry (battleaxes, swords, spears, warhammers) excepting fire.
So, my question is, How Can A Creature Or Object Gain the Strengthen Enchantment?
- Gaining the Enchantment: As stated above, an item must kill a Whackagi in order to gain the Strengthen Enchantment. By definition, that means it must inflict lethal damage to a nearly invulnerable monstrosity. The most likely method would be by suffocation or by wielding the item when it is red-hot.
Creatures have it a tiny bit easier; a creature (I'm thinking medieval European here, maybe a dog since they can help fight monsters) can gain the Enchantment by either killing it with their natural weaponry, killing it with a weapon incorporating their own body (like a club studded with baby teeth or a bone steel sword forged with one's own bone), or by being alive inside it when it is killed. As stated in Unconventional Rebirth: Is It Checked?, gaining the Enchantment naturally heals a creature qualifying for the latter.
A quick list of weaknesses: Whackagi cannot bend and are therefore made brittle (prone to snapping or shattering) in temperatures below freezing (such as in an icy lake), fire burns them up, and while they have a decentralized nervous system, this can, in fact, be foiled rather easily. Crushing or flattening them won't kill them, but the resulting suffocation (from the object on top of them) can and will (since it's rather hard to wriggle out from under something crushing you flat, like a boulder). Finally, Whackagi can breathe underwater, so drowning is out.
Answers must be feasible for medieval Europeans, something they can not only come up with but actually enact. The best answer will have the most efficient method(s); ie. the method requiring the least time, labor, and resources to enchant an item, human, or dog.